//#pragma GCC optimize("Ofast", "unroll-loops")
//#pragma GCC target("sse", "sse2", "sse3", "ssse3", "sse4")

#include <bits/stdc++.h>

#define all(a) a.begin(),a.end()
#define len(a) (int)(a.size())
#define mp make_pair
#define pb push_back
#define fir first
#define sec second
#define fi first
#define se second

using namespace std;

typedef pair<int, int> pii;
typedef long long ll;
typedef long double ld;

template<typename T>
bool umin(T &a, T b) {
    if (b < a) {
        a = b;
        return true;
    }
    return false;
}
template<typename T>
bool umax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

#ifdef KIVI
#define DEBUG for (bool _FLAG = true; _FLAG; _FLAG = false)
#define LOG(...) print(#__VA_ARGS__" ::", __VA_ARGS__) << endl
template <class ...Ts> auto &print(Ts ...ts) { return ((cerr << ts << " "), ...); }
#else
#define DEBUG while (false)
#define LOG(...)
#endif

const int max_n = -1, inf = 1000111222;

inline void test_case () {
    string a, b;
    cin >> a >> b;
    if (a == b) {
        cout << "0\n";
        return;
    }
    if (len(a) == 1 || len(b) == 1) {
        cout << "-1\n";
        return;
    }
    int n = len(a);
    vector <pii> ans;
    auto op = [&] (int l, int r) {
        ans.pb({l, r});
    };
    for (int i = 1; i < n; i++) {
        if (a[i] == '0') {
            a[i] = '1';
            op(i - 1, i);
        }
    }
    while (n > len(b)) {
        op(n - 2, n - 1);
        op(n - 3, n - 2);
        op(n - 2, n - 1);
        op(n - 3, n - 2);
        --n;
        a.pop_back();
    }
    while (n < len(b)) {
        op(n - 2, n - 1);
        op(n - 2, n - 1);
        op(n - 1, n);
        ++n;
        a += '1';
    }
    assert(n == len(b));
    for (int i = n - 1; i >= 0; i--) {
        if (b[i] == '0') {
            op(i - 1, i);
            op(i, i + 1);
        }
    }
    cout << len(ans) << '\n';
    for (auto &i : ans) {
        cout << i.first + 1 << ' ' << i.second + 1 << '\n';
    }
}

int main() {
//    freopen("input.txt", "r", stdin);
//    freopen("output.txt", "w", stdout);

    ios_base::sync_with_stdio(0);
    cin.tie(0);

    int t = 1;
    cin >> t;
    for (int test = 1; test <= t; test++) {
        test_case();
    }
}