#include <bits/stdc++.h>

#define int long long 
#define pii pair < int , int >

using namespace std;

const int N = 64 + 10;

void Solve()
{
    vector < int > a, b;
    string s, t;
    int n, m;
    cin >> s >> t;
    vector < pii > ans;
    for (auto si : s)
        a.push_back(si - '0');
    for (auto ti : t)
        b.push_back(ti - '0');
    //

    n = (int)a.size();
    for (int i = n - 1; i >= 1; i--)
    {
        if (a[i] == 1 && a[i - 1] == 1)
        {
            ans.push_back({i - 1, i});
            ans.push_back({i, i + 1});
            a[i] = 0;
        }
    }

    // for (auto ai : a)
    //     cerr << ai;
    // cerr << "\n";

    // 00 -> 0
    n = (int)a.size(), m = (int)b.size();
    for (int i = 0; i < n - 1; i++)
    {
        if (a[i] == 0 && a[i + 1] == 0)
        {
            ans.push_back({i, i + 1});
            a.erase(a.begin() + i);
            n--;
        }
    }

    // for (auto ai : a)
    //     cerr << ai;
    // cerr << "\n";

    if ((int)a.size() > (int)b.size() || ((int)a.size() == 1 && a != b))
    {
        cout << -1 << "\n";
        return ;
    }

    // 10 -> 11
    n = (int)a.size(), m = (int)b.size();
    for (int i = 0; i < n - 1; i++)
    {
        if (a[i] == 1 && a[i + 1] == 0)
        {
            ans.push_back({i, i + 1});
            a[i + 1] = 1;
        }
    }

    // n -> m

    int ct = (int)b.size() - (int)a.size();
    for (int i = 1; i <= ct; i++)
    {
        n = (int)a.size() - 1;
        ans.push_back({n - 1, n});
        ans.push_back({n - 1, n});
        ans.push_back({n, n + 1});
        a.push_back(1);
    }

    n = (int)a.size();
    for (int i = 0; i < n; i++)
    {
        if (b[i] == 0)
        {
            ans.push_back({i - 1, i});
            ans.push_back({i, i + 1});
            a[i] = 0;
        }
    }
    
    assert(ans.size() <= 512);
    cout << ans.size() << "\n";
    for (auto [l, r] : ans)
        cout << l + 1 << " " << r + 1 << "\n";
    return ;

}

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

    int T = 1;
    cin >> T;

    while (T--)
    {
        Solve();
    }
}