#include <bits/stdc++.h>
using namespace std;
const int maxn = 100 + 5;
int T;
char a[maxn], b[maxn];
vector < pair <int, int> > ans;
int main () {
	cin >> T;
	while (T--) {
		ans.clear ();
		cin >> a + 1;
		cin >> b + 1;
		int s, t;
		s = strlen (a + 1), t = strlen (b + 1);
		if (s == 1 || t == 1) {
			puts ("-1");
			continue;
		}
		for (int i = 1; i < s; i++) if (a[i + 1] == '0') ans.push_back (make_pair (i, i + 1));
		if (s > t) 
		while (s > t) {
			ans.push_back (make_pair (s - 2, s - 1));
			ans.push_back (make_pair (s - 1, s + 1));
			s--;
		}
		else 
		while (s < t) {
			ans.push_back (make_pair (s - 1, s));
			ans.push_back (make_pair (s - 1, s));
			ans.push_back (make_pair (s, s + 1));
			s++;
		}
		for (int i = 1; i <= t; i++) 
		if (b[i] == '0') {
			ans.push_back (make_pair (i - 1, i));
			ans.push_back (make_pair (i, i + 1));
		}
		cout << ans.size () << '\n';
		for (auto v : ans) cout << v.first << ' ' << v.second << '\n';
	}
	return 0;
}