#include<bits/stdc++.h>
using namespace std;
using i64 = long long;
void work() {
	string A, B;
	cin >> A >> B;
	int lb = B.length();
	if(A.length() == 1 && B.length() == 1) {
		if(A == B) cout << "0\n";
		else cout << "-1\n";
		return;
	}
	if(A.length() == 1 || B.length() == 1) {
		cout << "-1\n";
		return;
	}
	vector<pair<int, int>> ans;
	for(int i = 0; i < A.size(); ++i) {
		if(A[i] == '0') ans.emplace_back(i, i + 1), A[i] = '1';
	}
	while(A.length() < lb) {
		ans.emplace_back(A.length() - 1, A.length());
		ans.emplace_back(A.length() - 1, A.length());
		A += '1';
		ans.emplace_back(A.length() - 1, A.length());
	}
	if(A.length() > lb) {
		ans.emplace_back(A.length() - 1, A.length());
		A.pop_back();
		while(A.length() > lb - 1) {
			ans.emplace_back(A.length() - 1, A.length());
			ans.emplace_back(A.length(), A.length() + 1);
			A.pop_back();
		}
//		ans.emplace_back(99999, 99999);
		ans.emplace_back(A.length() + 1, A.length() + 2);
		ans.emplace_back(A.length(), A.length() + 1);
	}

//	cout << A << "\n";
	for(int i = lb - 1; i >= 0; --i) {
		if(B[i] == '0') {
			ans.emplace_back(i, i + 1);
			ans.emplace_back(i + 1, i + 2);
			A[i] = '0';
		}
	}
//	cout << A << "\n" << B << "\n";
//	if(A != B || ans.size() > 500) while(1);
	cout << ans.size() << "\n";
	for(auto i : ans) {
		cout << i.first << " " << i.second << "\n";
	}
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	int t;
	cin >> t;
	while(t--)
		work();
}