#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
const int maxn = 2e6 + 5;

int cnt[250];
char s[maxn], t[maxn], ss[maxn], tt[maxn];
int op[maxn], nl[maxn], nr[maxn];
int pre[maxn], suf[maxn];

int c[maxn << 1], ans[maxn << 1], ansl, clen, aL, aR, aot;

void clear()
{
    for (int i = clen; ~i; i--) c[i] = 0;
    clen = 0;
}

void add(int x, int y)
{
    clen = max(clen, y - x);
    for (int i = y; i >= x; i--) c[y - i] += s[i] - '0';
    for (int i = 0; i <= clen; i++)
        if (c[i] >= 10)
        {
            if (i == clen) clen++;
            c[i + 1] += c[i] / 10, c[i] %= 10;
        }
}

void upd(int t)
{
    c[0] += t;
    int nw = 0;
    while (c[nw] >= 10)
    {
        if (nw == clen) clen++;
        c[nw + 1] += c[nw] / 10; c[nw] %= 10;
        nw++;
    }
}

void compare(int L, int R, int ot)
{
    if (clen < ansl) return;
    if (clen > ansl)
    {
        ansl = clen;
        for (int i = ansl; ~i; i--) ans[i] = c[i];
        aL = L, aR = R, aot = ot;
        return;
    }

    for (int i = ansl; ~i; i--)
    {
        if (c[i] > ans[i])
        {
            for (int j = i; ~j; j--) ans[j] = c[j];
            aL = L, aR = R, aot = ot;
            return;
        }
        else if (c[i] < ans[i]) break;
    }
    aL = L, aR = R, aot = ot;
}

void work()
{
    int n; cin >> n >> s + 1 >> t + 1;
    for (int i = 1; i <= 2 * n; i++) ss[i] = s[i], tt[i] = t[i];
    for (int i = 1; i <= n; i++) op[i] = -1, nl[i] = nr[i] = 0;
    int mx1 = 0, mn2 = n + 1;
    for (int i = 1; i <= 2 * n; i += 2)
    {
        int x = i / 2 + 1;
        cnt['1'] = cnt['2'] = cnt['?'] = 0;
        cnt[s[i]]++, cnt[t[i]]++, cnt[s[i + 1]]++, cnt[t[i + 1]]++;
        if (cnt['1'] > 1 || cnt['2'] > 1)
        {
            cout << "impossible\n";
            return;
        }
        if (s[i + 1] == '?' && t[i + 1] == '?' && cnt['1'] && cnt['2']) mx1 = max(mx1, x), nl[x] = 1;
        else if (s[i] == '?' && t[i] == '?' && cnt['1'] && cnt['2']) mn2 = min(mn2, x), nr[x] = 1;

        if (s[i + 1] == '?' && t[i + 1] == '?') nl[x] = 1;
        if (s[i] == '?' && t[i] == '?') nr[x] = 1;

        if (!cnt['1'] && !cnt['2']) op[x] = -1;
        if (cnt['1'])
        {
            if (s[i] == '1' || t[i] == '1') op[x] = 1;
            else op[x] = 0;
        }
        if (cnt['2'])
        {
            if (s[i] == '2' || t[i] == '2') op[x] = 0;
            else op[x] = 1;
        }
    }

    for (int i = 1; i < 2 * n; i++)
        if (s[i] != '?' && s[i] == s[i + 1] || t[i] != '?' && t[i] == t[i + 1] || s[i] != '?' && s[i] == t[i + 1] || t[i] != '?' && t[i] == s[i + 1])
        {
            cout << "impossible\n";
            return;
        }
    
    for (int i = ansl; ~i; i--) ans[i] = 0;
    ansl = 0, aL = aR = -1;

    int L = 0, R = n + 1;
    while (nl[L + 1]) L++;
    while (nr[R - 1]) R--;
    suf[n + 1] = 0;
    for (int i = 1; i <= L; i++) pre[i] = pre[i - 1] + (s[2 * i - 1] != '?' ? s[2 * i - 1] - '0' : (t[2 * i - 1] != '?' ? '3' - t[2 * i - 1] : 2));
    for (int i = n; i >= R; i--) suf[i] = suf[i + 1] + (s[2 * i] != '?' ? s[2 * i] - '0' : (t[2 * i] != '?' ? '3' - t[2 * i] : 2));

    if (L >= R - 1)
    {
        clear();
        upd(pre[L] + suf[L + 1]);
        compare(L + 1, L, 0);
    }


    int l = mx1 + 1, lstl = mx1 + 1;
    while (l < mn2)
    {
        int r = l, p = op[l];
        while (r + 1 < mn2)
        {
            if (p == -1)
            {
                p = op[r + 1];
                r++;
                continue;
            }
            if (op[r + 1] == -1) r++;
            else if (p == op[r + 1]) r++;
            else break;
        }

        if (l > L + 1 || r < R - 1 || l <= mx1 || r >= mn2)
        {
            lstl = r + 1;
            while (op[lstl - 1] == -1) lstl--;
            l = r + 1;
            continue;
        }

        for (int i = lstl; i < l; i++) s[2 * i - 1] = s[2 * i] = t[2 * i - 1] = t[2 * i] = '?';
        int opt = p; l = lstl;
        for (int i = l; i <= r; i++)
            if (opt == -1) s[2 * i - 1] = '2', s[2 * i] = '1';
            else
            {
                if (s[2 * i - 1] == '?' && t[2 * i - 1] == '?')
                {
                    if (opt == 0) s[2 * i - 1] = '2';
                    else s[2 * i - 1] = '1';
                }
                if (s[2 * i] == '?' && t[2 * i] == '?')
                {
                    if (opt == 0) s[2 * i] = '1';
                    else s[2 * i] = '2';
                }
            }
        
        int x = 2 * l - 1;
        clear();
        while (x <= 2 * r)
        {
            if (s[x] == '?')
            {
                x++;
                continue;
            }
            int y = x;
            while (y < 2 * r && s[y + 1] != '?') y++;
            add(x, y);
            x = y + 1;
        }
        upd(pre[l - 1] + suf[r + 1]);
        compare(l, r, opt);
        lstl = r + 1;
        while (op[lstl - 1] == -1) lstl--;
        l = r + 1;
    }

    if (aL == -1 && aR == -1)
    {
        cout << "impossible\n";
        return;
    }

    for (int i = ansl; ~i; i--) cout << ans[i]; cout << "\n";
    for (int i = 1; i <= 2 * n; i++) s[i] = ss[i], t[i] = tt[i];
    
    for (int i = 1; i < aL; i++)
    {
        int x = pre[i] - pre[i - 1];
        s[2 * i - 1] = '0' + x, t[2 * i - 1] = '3' - x;
    }

    for (int i = aR + 1; i <= n; i++)
    {
        int x = suf[i] - suf[i + 1];
        s[2 * i] = '0' + x, t[2 * i] = '3' - x;
    }

    for (int i = aL; i <= aR; i++)
        if (aot == -1) s[2 * i - 1] = '2', s[2 * i] = '1';
        else
        {
            if (s[2 * i - 1] == '?' && t[2 * i - 1] == '?')
            {
                if (aot == 0) s[2 * i - 1] = '2';
                else s[2 * i - 1] = '1';
            }
            if (s[2 * i] == '?' && t[2 * i] == '?')
            {
                if (aot == 0) s[2 * i] = '1';
                else s[2 * i] = '2';
            }
        }
    
    for (int i = 1; i <= 2 * n; i++) cout << (s[i] == '?' ? '0' : s[i]); cout << "\n";
    for (int i = 1; i <= 2 * n; i++) cout << (t[i] == '?' ? '0' : t[i]); cout << "\n";
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);

    int T;
    cin >> T;
    while (T--) work();
    return 0;
}