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

using ll = long long;

string operator+(string a, string b) {
    if(a.size() < b.size()) swap(a, b);
    if(b.size() == a.size()) a.push_back('0');
    int flg = 0;
    // cerr << a << "|" << b << '\n';
    for(int i = 0; i < b.size(); i++) {
        int now = a[i] - '0' + b[i] - '0' + flg;
        a[i] = now % 10 + '0', flg = now / 10;
    }
    for(int i = b.size(); i < a.size() && flg; i++) {
        int now = a[i] - '0' + flg;
        a[i] = now % 10 + '0', flg = now / 10;
    }
    while(a.size() && a.back() == '0') a.pop_back();
    return a;
}
string operator+(string a, int b) {
    string c = to_string(b);
    reverse(c.begin(), c.end());
    return a + c;
}
bool operator<(string a, string b) {
    if(a.size() != b.size()) return a.size() < b.size();
    for(int i = (int)a.size() - 1; i >= 0; i--) {
        if(a[i] != b[i]) return a[i] < b[i];
    }
    return 1;
}

void solve() {
    int n;
    string s[2];
    cin >> n >> s[0] >> s[1];
    vector<array<int, 4>> ve(n + 1);
    for(int i = 1; i <= n; i++) {
        auto calc = [&](char ch) {
            if(ch == '?') return 0;
            else return ch - '0';
        };
        ve[i] = {
            calc(s[0][2 * i - 2]),
            calc(s[1][2 * i - 2]),
            calc(s[0][2 * i - 1]),
            calc(s[1][2 * i - 1]),
        };
        int cnt[3] = {0, 0};
        for(auto j : ve[i]) {
            cnt[j]++;
        }
        if(cnt[1] > 1 || cnt[2] > 1) {
            cout << "impossible\n";
            return;
        }
    }
    // for(int i = 1; i <= n; i++) {
    //     auto [a, b, c, d] = ve[i];
    //     // cerr << a << ' ' << b << ' ' << c << ' ' << d << '\n';
    // }
    int l = 0, r = n + 1;
    for(int i = 1; i <= n; i++) {
        auto [a, b, c, d] = ve[i];
        if(a && b) l = i;
        if(c && d && r == n + 1) r = i;
    }
    if(l > r) {
        cout << "impossible\n";
        return;
    }
    vector<int> pre(n + 1), suf(n + 2);
    for(int i = 1; i <= n; i++) {
        auto [a, b, c, d] = ve[i];
        if(c || d) pre[i] = -1e9;
        else if(b == 2 || a == 1) pre[i] = pre[i - 1] + 1;
        else pre[i] = pre[i - 1] + 2;
    }
    for(int i = n; i; i--) {
        auto [a, b, c, d] = ve[i];
        if(a || b) suf[i] = -1e9;
        else if(d == 2 || c == 1) suf[i] = suf[i + 1] + 1;
        else suf[i] = suf[i + 1] + 2;
    }
    vector<int> ty(n + 1);
    for(int i = l + 1; i < r; i++) {
        auto [a, b, c, d] = ve[i];
        int L = max(a, b), R = max(c, d);
        if(!(L == 1 || R == 2)) ty[i] |= 2; // 1 -> 2 1
        if(!(L == 2 || R == 1)) ty[i] |= 1; // 2 -> 1 2
    }
    auto neg = [&](int x) {
        return x == 1 ? 2 : 1;
    };
    auto add = [&](int len, int beg, string &now) {
        string ad;
        for(int i = 0, t = beg; i < len; i++) {
            ad += t + '0';
            t = neg(t);
        }
        reverse(ad.begin(), ad.end());
        now = now + ad;
    };
    string ans;
    int L = -1, R = -1, Ty = -1, ff = 0;
    for(int i = l; i < r; i++) {
        // cerr << pre[i] << ' ' << suf[i + 1] << '\n';
        if(pre[i] >= 0 && suf[i + 1] >= 0) {
            string now = to_string(pre[i] + suf[i + 1]);
            reverse(now.begin(), now.end());
            // string now;
            // now = now + pre[i] + suf[i + 1];
            // cerr << now << '\n';
            if(ans < now) {
                ff = 1;
                ans = now, L = i + 1, R = i;
            }
        }
    }
    for(int fuck = 1; fuck <= 2; fuck++) {
        for(int i = l + 1, j; i < r; i = j + 1) {
            j = i;
            if(!(ty[i] & fuck)) continue;
            while(j + 1 < r && (ty[j + 1] & fuck)) j++;
            if(pre[i - 1] < 0 || suf[j + 1] < 0) continue;
            string now;
            int len = 0, beg = fuck;
            for(int k = i; k <= j; k++) {
                auto [a, b, c, d] = ve[k];
                if(b == fuck) {
                    add(len, beg, now), len = 0, beg = neg(fuck);
                } else len++;
                if(d == neg(fuck)) {
                    add(len, beg, now), len = 0, beg = fuck;
                } else len++;
            }
            add(len, beg, now);
            now = now + pre[i - 1] + suf[j + 1];
            if(ans < now) {
                ans = now, L = i, R = j, Ty = fuck;
                ff = 1;
            }
        }
    }
    if(ff && ans.empty()) ans = "0";
    if(ans.empty()) {
        cout << "impossible\n";
        return;
    }
    reverse(ans.begin(), ans.end());
    // cerr << L << ' ' << R << ' ' << Ty << '\n';
    cout << ans << '\n';
    string tab[2];
    tab[0] = tab[1] = string(2 * n, '0');
    for(int i = 1; i < L; i++) {
        auto [a, b, c, d] = ve[i];
        if(b != 2 && a != 1) {
            tab[0][2 * i - 2] = '2';
            tab[1][2 * i - 2] = '1';
        } else {
            tab[0][2 * i - 2] = '1';
            tab[1][2 * i - 2] = '2';
        }
    }
    for(int i = L; i <= R; i++) {
        auto [a, b, c, d] = ve[i];
        if(b != Ty) {
            tab[0][2 * i - 2] = Ty + '0';
        } else {
            tab[1][2 * i - 2] = Ty + '0';
        }
        if(d != neg(Ty)) {
            tab[0][2 * i - 1] = neg(Ty) + '0';
        } else {
            tab[1][2 * i - 1] = neg(Ty) + '0';
        }
    }
    for(int i = R + 1; i <= n; i++) {
        auto [a, b, c, d] = ve[i];
        if(d != 2 && c != 1) {
            tab[0][2 * i - 1] = '2';
            tab[1][2 * i - 1] = '1';
        } else {
            tab[0][2 * i - 1] = '1';
            tab[1][2 * i - 1] = '2';
        }
    }
    cout << tab[0] << '\n' << tab[1] << '\n';
}
signed main() {
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    int t = 1;
    cin >> t;
    while(t--) solve();
    return 0;
}
/*
1
4
1???????
???2???2

5
2
?1??
??1?
4
1???????
???2???2
5
??????????
??????????
6
1212????????
????????1212
7
?2?1?????1?2??
?????1???????2

1
2
1??1
2??2

*/