#include <iostream>
#include <string>
#include <vector>
#include <utility>
using namespace std;

void work();

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

void work()
{
	string x, y;
	cin >> x >> y;
	if (x == y)
	{
		cout << "0\n";
		return;
	}
	if (x == "1" || y == "1")
	{
		cout << "-1\n";
		return;
	}
	vector<pair<int, int>> ans;
	for (int i = 0; i < x.size(); i++)
	{
		if (x[i] == '0')
		{
			x[i] = '1';
			ans.push_back(make_pair(i - 1, i));
		}
	}
	if (x.size() > y.size())
	{
		int t = x.size() - y.size();
		for (int i = 0; i <= t; i++)
			ans.push_back(make_pair(x.size() - i - 2, x.size() - i - 1));
		ans.push_back(make_pair(x.size() - t - 1, x.size() + t));
		ans.push_back(make_pair(x.size() - 2, x.size() - 1));
		while (x.size() > y.size())
			x.pop_back();
	}
	while (x.size() < y.size())
	{
		ans.push_back(make_pair(x.size() - 2, x.size() - 1));
		ans.push_back(make_pair(x.size() - 2, x.size() - 1));
		ans.push_back(make_pair(x.size() - 1, x.size()));
		x.push_back('1');
	}
	for (int i = 0; i < x.size(); i++)
	{
		if (y[i] == '0')
		{
			ans.push_back(make_pair(i - 1, i));
			ans.push_back(make_pair(i, i + 1));
			x[i] = '0';
		}
	}
	cout << ans.size() << '\n';
	for (auto i : ans)
	{
		cout << i.first + 1 << ' ' << i.second + 1 << '\n';
	}
	return;
}