#include <bits/stdc++.h>

using namespace std;

#define mp make_pair
const bool TEST = true;
struct S{
	string s;
	vector<pair<int,int>> ans;
	int cntB1;
	string hiddens;

	string myA,myB;
	string change(const string& s){
		// cout << "change: " << s;
		int num = 0;
		int mul = 1;
		for (int i = s.size()-1; i >= 0; --i){
			num += (s[i]-'0')*mul;
			mul *= 3;
		}
		string ret;
		if (num == 0) {
			ret.push_back('0');
		}
		while(num){
			ret.push_back((num&1)+'0');
			num >>= 1;
		}

		reverse(ret.begin(),ret.end());
		// cout << " " << ret << endl;
		return ret;
	}

	void outputans(){
		// return ;
		assert(hiddens == myB);
		// assert(ans.size() <= 512);
		// return ;
		cout << ans.size() << "\n";
		for(auto [x,y] : ans){
			cout << x << " " << y << "\n";
		}

	}
	void addans(int x,int y){
		// cout << "op: " << x << " " << y << endl;
		// cout << hiddens << endl << "\n";
		if (x < 0 || y < 0){
			cout << myA << " " << myB << endl;
		}
		assert(x >= 0 && y >= 0);
		// cout << "concentation: " << endl;
		// cout << hiddens.substr(0,x) << endl;
		// cout << change(hiddens.substr(x,y-x+1)) << endl;
		// cout << hiddens.substr(y+1,hiddens.size()-1-y) << endl;
		// cout << "ENDcon" << endl;
		if (TEST){
			hiddens = hiddens.substr(0,x)+change(hiddens.substr(x,y-x+1))+hiddens.substr(y+1,hiddens.size()-1-y);
		}
		// cout << hiddens << endl;
		ans.push_back(mp(x+1,y+1));
		
	}

	bool sol(const string& A,const string& B){
		myA = A; myB = B;
		if (A.size() == 1) {
			if (B.size() == 1){ cout << 0 << "\n";}
			else {cout << -1 << "\n";}
			return false;
		}
		if (B.size() == 1){
			cout << -1 << "\n";
			return false;
		}
		ans.clear();
		cntB1 = 0;
		for (auto ch : B){
			if (ch == '1') cntB1++;
		}
		hiddens = A;
		s = A;
		for (int i = 0; i < s.size(); ++i){
			if (s[i] == '0'){
				addans(i-1,i);
				s[i] = '1';
			}
		}
		// 变为全1
		// cout << "FULL1: " << hiddens << endl;
		// cout << "cntB1: " << cntB1 << endl;
		// return false;
		int cntA1 = s.size();

		if (cntB1 == 1){
			while(cntA1 != 2){
				addans(s.size()-3,s.size()-2);
				addans(s.size()-1,s.size());
				addans(s.size()-2,s.size()-1);
				s.pop_back();
				cntA1--;
			}
			// cout << "s: " << s << endl;
			int cnt0 = B.size()-1;
			addans(0,1);
			for(cnt0 = 2; cnt0 < B.size()-1; ++cnt0){
				addans(0,1);
				addans(0,1);
				s.push_back('0');
			}
			// if (hiddens != B){
			// 	cout << "WA:" << endl;
			// 	cout << "A:" << A << endl << "B: " << B << endl << "ANS: " << hiddens << endl;
			// }
			outputans();
			return false;
		}
		//留到cntB1个1
		if (cntA1 < cntB1){
			while(cntA1 != cntB1){
				addans(s.size()-2,s.size()-1);
				addans(s.size()-2,s.size()-1);
				s.push_back('1');
				addans(s.size()-2,s.size()-1);
				cntA1++;
			}
		} else if (cntA1 > cntB1){
			while(cntA1 != cntB1){
				addans(s.size()-3,s.size()-2);
				addans(s.size()-1,s.size());
				addans(s.size()-2,s.size()-1);
				s.pop_back();
				cntA1--;
			}
		}
		// cout << "cntB1 1: " << hiddens << endl;

		//加上B从后往前的0
		int last1ind = B.size()-1;
		int start = s.size()-2;
		for (;B[last1ind] == '0'; --last1ind){
			addans(start,start+1);
			addans(start,start+1);
			s.push_back('0');
		}
		// cout << "ADD SUF 0: " << hiddens << endl;
		// cout << last1ind << endl;
		// return false;
		int ind = 0;
		while(ind != last1ind){
			while(B[ind+1] == '1'){
				ind++;
			}

			if (ind == last1ind) break;
			// ind--;
			int nxt1;
			for (nxt1 = ind+1; B[nxt1] != '1'; ++nxt1) {}
			addans(ind,ind+1);
			addans(ind,ind+1);
			addans(ind+1,ind+2);
			addans(ind,ind+1);
			if (nxt1 - ind == 2){
				addans(ind+1,ind+2);
			} else {
				for (int zcnt = 3; zcnt <= nxt1-ind-1; ++zcnt){
					addans(ind,ind+1);
					addans(ind,ind+1);
				}
			}
			ind = nxt1;
		}
		// if (hiddens != B){
		// 	cout << "WA:" << endl;
		// 	cout << "A:" << A << endl << "B: " << B << endl << "ANS: " << hiddens << endl;
		// }
		// cout << "ans: " << hiddens << "\n";
		outputans();
		return true;
	}

} sct;





void solve(){
	string A,B;
	cin >> A >> B;
	// int la = rand()%10+2;
	// int lb = rand()%10+2;
	// A.push_back('1');
	// B.push_back('1');
	// for (int i = 0; i < la; i++){
	// 	A.push_back('0'+(rand()%2));
	// }
	// for (int i = 0; i < lb; i++){
	// 	B.push_back('0'+(rand()%2));
	// }
	// cout << A << " " << B << endl;
	sct.sol(A,B);


}
int main(){
	srand(time(0));
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int T;cin >> T;
	// int T = 1;
	while(T--){
		solve();
	}
	return 0;
}