//#define _CRT_SECURE_NO_WARNINGS 1
#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <string>
#include <queue>
#include <vector>
#include <map>
#include <set>
#include <unordered_map>
#include <stack>
#include <ctime>
#include <cstdlib>
#include <cstdio>
#include <iomanip>
#include <climits>
#include <random>
using namespace std;
#define ll long long
#define pii pair<int,int>
#define pll pair<ll,ll>
#define lowbit(x) (x&-x)
#define ls k<<1
#define rs (k<<1)|1
#define mid ((l+r)>>1)
#define all(x) s.begin(),x.end()
#define fi first
#define se second
#define pb push_back
#define all(x) x.begin(),x.end()
#define LYLNB ios::sync_with_stdio(false); cin.tie(0); cout.tie(0)
typedef unsigned long long u64;
//#define int long long 
string s, t;
vector<pii>ans;
void w(int l, int r) { ans.push_back({ l,r }); }
void solve() {
    cin >> s >> t;
    int n = s.length(), m = t.length();
    if (n == 1 || m == 1) {
        if (n == 1 && m == 1 && s[0] == t[0]) {
            cout << 0 << endl;
        }
        else cout << -1 << endl;
        return;
    }
    for (int i = 2; i <= n; i++) {
        if (s[i - 1] == '0') {
            w(i - 1, i);
        }
    }
    if (n > m) {
        for (int i = 1; i <= n - m; i++) {
            w(1, 2); w(2, 3); w(1, 2);
        }
    }
    else{
        for (int i = 1; i <= m - n; i++) {
            w(1, 2); w(1, 2); w(2, 3);
        }
    }
    for (int i = 2; i <= m; i++) {
        if (t[i - 1] == '0') {
            w(i - 1, i); w(i, i + 1);
        }
    }
    cout << ans.size() << endl;
    for (pii p : ans)cout << p.first << " " << p.second << endl;
    ans.clear();
}
signed main() {
    LYLNB;
    int T = 1; cin >> T;
    while (T--) {
        solve();
    }
    return 0;
}