#include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pii;
typedef long long ll;
typedef ll i64;
typedef __int128 i128;
constexpr int maxn=5e5+9;
string a,b;
int n,m;
void solve()
{
    vector<pii> ans;
    cin>>a>>b;
    n=a.length();
    m=b.length();
    if(a==b)
    {
        puts("0");
        return;
    }
    if(n==1) { puts("-1"); return; }
    a="@"+a; b="@"+b;
    int tot=0;
    int last1=-1,sum1=0;
    for(int i=n;i;--i)
    {
        if(a[i]=='0')
            if(last1==-1) ++tot;
            else ;
        else
        {
            if(last1!=-1 && last1!=i+1)
                ans.push_back({i+1,last1});
            last1=i; ++sum1;
        }
    }
    if(last1>1) ans.push_back({1,last1});
    // ans.push_back({sum1+1,sum1+tot});
    // 111..100...0
    for(int i=0;i<tot;++i) ans.push_back({sum1+i,sum1+i+1});
    // 111........1
    sum1+=tot;
    // to length m
    while(sum1>m)
    {
        --sum1;
        ans.push_back({1,2});
        ans.push_back({2,4});
    } // what if sum1<4 a.k.a. sum1==3
    // 111 -> 1001 -> 11 thats ok
    if(sum1<m)
    {
        ans.push_back({1,2});
        ans.push_back({1,3});
        while(sum1<m)
        {
            ++sum1;
            ans.push_back({1,3});
        }
        ans.push_back({2,4});
    }
    for(int i=m;i;--i)
        if(b[i]=='0')
        {
            ans.push_back({i-1,i});
            ans.push_back({i,i+1});
        }
    printf("%d\n",ans.size());
    for(auto[l,r]:ans) printf("%d %d\n",l,r);
}
int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0); cout.tie(0);
    int t=1;
    cin>>t;
    while(t--) solve();
    return 0;
}