#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');

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

    // 0 -> 1
    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;
        }
    }

    //1->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});
            a[i] = 0;
            a.push_back(0);
        }
    }

    //n -> m
    n = (int)a.size(), m = (int)b.size();
    while (n > m)
    {
        ans.push_back({n - 2, n - 1});
        n--;
        a.pop_back();
    }

    while (n < m)
    {
        ans.push_back({0, 1});
        ans.push_back({0, 1});
        a.push_back(0);
        n++;
    }

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

    // 1->0
    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();
    }
}