#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
typedef pair<int,int> PII;
const int MX=1010;

int T, cnt;
PII op[MX];
int read()
{
    int r=0, f=1; char ch=getchar();
    while(ch<'0'||ch>'9') {if(ch=='-') f=-1; ch=getchar();}
    while(ch>='0'&&ch<='9') {r=r*10+ch-'0'; ch=getchar();}
    return r*f;
}
int main()
{
    // freopen("testdata.in","r",stdin);
    T=read();
    while(T--)
    {
        string s1, s2;
        // s1 -> 1111 -> s2
        cin >> s1;
        cin >> s2;
        int N=s1.size(); s1=" "+s1; 
        int M=s2.size(); s2=" "+s2;
        // cout << "N=" << N << ", M=" << M << '\n';
        if(N==1&&s1[1]=='1'&&M==1&&s2[1]=='1') {cout << "0\n"; continue;}
        if((N==1&&s1[1]=='1')||(M==1&&s2[1]=='1')) {cout << "-1\n"; continue;}
        cnt=0;
        for(int i=1;i<N;i++) // s1 -> 11111
        {
            // if(s1[i]=='1'&&s1[i+1]=='1') continue;
            if(s1[i]=='1'&&s1[i+1]=='0') 
            {
                op[++cnt]={i,i+1};
                s1[i+1]='1';
            }
        }
        // cout << "1...1\n";
        for(int i=N-2;i>=1;i--)
            op[++cnt]={i,i+1};
        op[++cnt]={2,N+N-2};
        // cout << "shrink done\n";
        for(int i=1,r=2;;i++)
        {
            op[++cnt]={i,r};
            r++;
            op[++cnt]={i,r};
            op[++cnt]={i,r};
            op[++cnt]={i,r};
            if(r==M) break;
        }   
        // cout << "extend done\n";
        s1=" ";
        for(int i=1;i<=M;i++) s1+='1';
        for(int i=M;i>=1;i--)
        {
            if(s1[i]==s2[i]) continue;
            else
            {
                if(s1[i]=='1'&&s2[i]=='0')
                {
                    op[++cnt]={i-1,i};
                    op[++cnt]={i,i+1};
                    s1[i]='0';
                }
                else if(s1[i]=='0'&&s2[i]=='1')
                {
                    op[++cnt]={i-1,i};
                    s1[i]='1';
                }
            }
        }
        cout << cnt << '\n';
        for(int i=1;i<=cnt;i++)
        {
            auto [l,r]=op[i];
            cout << l << " " << r << '\n';
        }
    }
    return (0-0);
}