#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using db = double;
constexpr int mod = 998244353;
constexpr int N = 1e6 + 10;

void solve() {
    string s, t;
    cin >> s >> t;
    int n = s.size(), m = t.size();
    if (n == 1) {
        cout << (s == t ? 0 : -1) << "\n";
        return;
    }
    s = "." + s; t = "." + t;
    vector<pair<int, int>> ans;
    auto trans_11_to_10 = [&](int x) {
        ans.push_back({x, x + 1});
        ans.push_back({x + 1, x + 2});
    };
    auto trans_10_to_11 = [&](int x) {
        ans.push_back({x, x + 1});
    };
    auto trans_000_to_0 = [&](int l, int r) {
        ans.push_back({l, r});
    };
    auto trans_11_to_111 = [&](int x) {
        ans.push_back({x, x + 1});
        ans.push_back({x, x + 1});
        ans.push_back({x + 1, x + 2});
    };
    for (int i = 1; i <= n - 1; i++) {
        if (s[i + 1] == '0') trans_10_to_11(i);
    }
    for (int i = n - 1; i >= 1; i--) trans_11_to_10(i);
    trans_000_to_0(2, n);
    trans_10_to_11(1);
    for (int i = 1; i <= m - 2; i++) trans_11_to_111(i);
    for (int i = 1; i <= m; i++) {
        if (t[i] == '0' && (i == m || t[i + 1] == '1')) {
            trans_11_to_10(i - 1);
        }
    }
    for (int i = m - 1; i >= 1; i--) {
        if (t[i] == '0' && t[i + 1] == '0') {
            trans_11_to_10(i - 1);
        }
    }
    cout << ans.size() << "\n";
    for (auto [l, r] : ans) cout << l << ' ' << r << "\n";
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    int tt = 1;
    cin >> tt;
    while (tt--) {
        solve();
    }
    return 0;
}