#include<bits/stdc++.h>
#define int long long
#define endl '\n'
using namespace std;
const int M=1e6+9,inf=1e9;
vector<pair<int,int> > ans;
string ppa;
string sb(string x,int l,int r)
{
	string now;
	for(int i=l;i<=r;i++)
		now+=x[i];
	return now;
}
string get(string x)
{
	for(auto [l,r] : ans)
	{
		assert(l>=0&&l<x.size());
		assert(r>=0&&r<x.size());
		int num=0;
		for(int i=l;i<=r;i++)
			num*=3,num+=(x[i]-'0');
		string th;
		while(num)
		{
			char c=num%2+'0';
			th+=c;
			num/=2;
		}
		reverse(th.begin(),th.end());
		x=sb(x,0,l-1)+th+sb(x,r+1,x.size()-1);
	}
	return x;
}
void pri()
{
	cout<<ans.size()<<endl;
	for(auto [l,r] : ans)
		cout<<l+1<<" "<<r+1<<endl;
//	cout<<get(ppa)<<endl;
	return;
}
void solve()
{
	ans.clear();
	string a,b;
	cin>>a>>b;
	ppa=a;
	if(b.size()==1||a.size()==1)
	{
		if(a!=b)
			cout<<-1<<endl;
		else
			cout<<0<<endl;
		return;
	}
	for(int i=0;i<a.size();i++)
	{
		if(a[i]=='0')
		{
			ans.push_back({i-1,i});
			a[i]='1';
		}
	}
	int cnt=0;
	for(auto now : b)
	{
		if(now=='1')
			cnt++;
	}
	if(cnt==1)
	{
		int pcnt=a.size();
		pcnt-=2;
		a="11";
		for(int i=1;i<=pcnt;i++)
		{
			ans.push_back({0,1});
			ans.push_back({1,3});
		}
		ans.push_back({0,1});
		ans.push_back({1,2});
		a="10";
		pcnt=b.size();
		pcnt-=2;
		for(int i=1;i<=pcnt;i++)
		{
			ans.push_back({0,1});
			ans.push_back({0,1});
		}
		pri();
		return;
	}
	int pcnt=a.size();
	if(pcnt>=cnt)
	{
		pcnt-=cnt;
		for(int i=1;i<=pcnt;i++)
		{
			ans.push_back({0,1});
			ans.push_back({1,3});
		}
	}
	else
	{
		pcnt=cnt-pcnt;
		for(int i=1;i<=pcnt;i++)
		{
			ans.push_back({0,1});
			ans.push_back({0,1});
			ans.push_back({1,2});
		}
	}
//	cout<<get(ppa)<<endl;
	vector<int> pnum(100,0);
	int tcnt=0,tot=0;
	for(int i=b.size()-1;i>=0;i--)
	{
		if(b[i]=='1')
		{
			pnum[++tot]=tcnt;
			tcnt=0;
		}
		else
			tcnt++;
	}
	for(int i=1;i<=pnum[1];i++)
	{
		int pos=cnt-i-1;
		ans.push_back({pos,pos+1});
		ans.push_back({pos,pos+1});
	}
	for(int i=2;i<=cnt;i++)
	{
		int pos=cnt-i;
		for(int j=1;j<=pnum[i];j++)
		{
			ans.push_back({pos,pos+1});
			ans.push_back({pos,pos+2});
			ans.push_back({pos+2,pos+3});
		}
	}
	pri();
}

signed main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	int T;
	cin>>T;
	while(T--)
		solve();
}