#define _CRT_SECURE_NO_WARNINGS 1
#pragma warning(disable:6031)
#include<bits/stdc++.h>
using namespace std;
#define ll long long

string a,b;
queue<pair<int, int>>q;
map<string, int>m;
vector<int> dp(100030);

void ztoo(int x)
{
	q.push({x-1,x});
	a[x] = '1';
}
void otoz(int x)
{
	q.push({ x - 1,x });
	q.push({ x,x + 1 });
	a[x] = '0';


}
void p1(int num)
{
	while (num--)
	{
		q.push({ 1,3 });
		q.push({ 2,3 });
		a.push_back('1');
	}


}
void m1(int num)
{
	num++;
	int len = a.size()-1;
	int i = 0;

	while(num--)
	{
		i++;
		otoz(len - i);
		a.pop_back();
	
	}
	q.push({ len - num + 1,len });
	ztoo(len - num + 1);
	



}
void write()
{
	cout << q.size() << endl;
	while (!q.empty())
	{
		auto tmp = q.front();
		q.pop();
		cout << tmp.first << " " << tmp.second << endl;



	}



}


void solve()
{
	while (!q.empty())q.pop();
	cin >> a >> b;

	if (a.size() == 1 || b.size() == 1)
	{
		if (a != b)
		{
			cout << -1 << endl;
			return;


		}
		else
		{
			cout << 0 << endl;
			return;
		}


	}
	if (a == b)
	{

		cout << 0 << endl;
		return;

	}
	a = 'x' + a;
	b = 'x' + b;
	int len = a.size();
	for (int i = 1;i < len;i++)
	{
		if (a[i] == '0')ztoo(i);
	}
	if (a.size() > b.size())
	{
		int num = a.size() - b.size();
		m1(num);



	}
	else if (a.size() < b.size())
	{
		int num = b.size() - a.size();
		p1(num);


	}
	 len = b.size();
	for (int i = 1;i < len;i++)
	{
		
		 if (b[i] == '0')otoz(i);


	}
	write();



	return;
}



int main()
{
	int tt;
	cin >> tt;
	while (tt--)
		solve();





}