#include<iostream>
#include<cstdio>
#include<algorithm>
#include<string>
#include<cstring>
#include<cmath>
#include<set>
#include<map>
#include<vector>
#include<queue>
#include<unordered_map>
#include<stack>
using namespace std;
#define int long long
#define scanf scanf_s
typedef pair<int, int> PII;

const double ef = 1e-12;
const int INF = 0x3f3f3f3f3f3f3f3f;
#define rep(i,a, b) for(int i = a;i<=b;i++)
#define pre(i,a, b) for(int i = a;i>=b;i--)
const int N = 5e5 + 5;

string a, b;
int cnt;
int ans[600][2];
int n, m;

void cun(int x, int y)
{
    ans[++cnt][0] = x;
    ans[cnt][1] = y;
}

void init()
{
    rep(i, 1, n) {
        if (a[i] == '0') cun(i - 1, i);
    }
    pre(i, n, 2) cun(i - 1, i);
    cun(2, 2 * n - 1);
}

void solve()
{
    cin >> a;
    cin >> b;
    n = a.size();
    m = b.size();
    a = " " + a;
    b = " " + b;
    cnt = 0;
    if (n == 1)
    {
        if (a == b) {
            cout << 0 << endl;
        }
        else cout << -1 << endl;
        return;
    }
    if (m == 1)
    {
        cout << -1 << endl;
        return;
    }
    init();
    rep(i, 3, m) {
        cun(1, 2);
        cun(1, 2);
    }
    rep(i, 2, m) cun(i - 1, i);
    rep(i, 2, m)
    {
        if (b[i] == '0')
        {
            cun(i - 1, i);
            cun(i, i + 1);
        }
    }
    if (cnt >= 512) while (1);
    cout << cnt << endl;
    rep(i, 1, cnt) {
        cout << ans[i][0] << " " << ans[i][1] << endl;
    }
}
signed main()
{

    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    int t = 1;
    cin >> t;

    while (t--) {
        solve();
    }

    return  0;

}