#include <bits/stdc++.h>

using i64 = long long;

void solve() {
    std::string A, B;
    std::cin >> A >> B;

    if (A == B) {
        std::cout << 0 << "\n";
        return;
    }
    if (A.size() == 1 || B.size() == 1) {
        std::cout << -1 << "\n";
        return;
    }

    int a = A.size(), b = B.size();
    std::vector<std::pair<int, int>> ans;
    for (int i = a - 1; i >= 0; i -- ) {
        if (A[i] == '0') {
            int j = i;
            while (j >= 0 && A[j] == '0') {
                j -- ;
            }
            a -= i - j - 1;
            ans.emplace_back(j + 1, i);
            ans.emplace_back(j, j + 1);
            i = j + 1;
        }
    }

    while (a > b) {
        ans.emplace_back(a - 2, a - 1);
        ans.emplace_back(a - 3, a - 2);
        ans.emplace_back(a - 2, a + 1);
        ans.emplace_back(a - 3, a - 2);
        a -- ;
    }
    while (a < b) {
        ans.emplace_back(a - 2, a - 1);
        ans.emplace_back(a - 2, a - 1);
        ans.emplace_back(a - 1, a);
        a ++ ;
    }
    assert(a == b);

    for (int i = b - 1; i; i -- ) {
        if (B[i] == '0') {
            ans.emplace_back(i - 1, i);
            ans.emplace_back(i, i + 1);
        }
    }

    std::cout << ans.size() << "\n";
    for (auto [x, y] : ans) {
        std::cout << x + 1 << " " << y + 1 << "\n";
    }    
}

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

    int t;
    std::cin >> t;

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

    return 0;
}