#include <bits/stdc++.h>
using namespace std;
template <typename T>
bool vmin(T& a, T b) {
  return (a > b) ? (a = b, true) : (false);
}
template <typename T>
bool vmax(T& a, T b) {
  return (a < b) ? (a = b, true) : (false);
}
template <typename T>
T smax(T x) {
  return x;
}
template <typename T, typename... K>
T smax(T a, const K&... args) {
  return max(a, smax(args...));
}
template <typename T>
T smin(T x) {
  return x;
}
template <typename T, typename... K>
T smin(T a, const K&... args) {
  return min(a, smin(args...));
}
template <typename A, typename B>
ostream& operator<<(ostream& os, const pair<A, B>& z) {
  os << "(" << z.first << ", " << z.second << ')';
  return os;
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& a) {
  bool isfirst = true;
  os << "{";
  for (auto z : a) {
    if (!isfirst) {
      os << ", ";
    }
    os << z;
    isfirst = false;
  }
  os << '}';
  return os;
}
int T;
int n;
void solve() {
  vector<int> a, b;
  auto read = [&](vector<int>& v) {
    static char tmp[4005];
    scanf("%s", tmp);
    n = strlen(tmp);
    v.resize(n);
    for (int i = 0; i < n; i++) v[i] = tmp[i] - '0';
  };
  read(a);
  read(b);
  vector<int> c(3, 0);
  for (int i = 0; i < n; i += 2) {
    c[a[i] + a[i + 1]]++;
  }
  for (int i = 0; i < n; i += 2) {
    c[b[i] + b[i + 1]]--;
  }
  if (smin(c[0], c[1], c[2]) < 0) {
    puts("-1");
    return;
  }
  auto getsum = [&](vector<int>& a) {
    int sum = 0;
    for (int i = 0; i < n; i += 2) {
      if (a[i] + a[i + 1] == 1) {
        sum = sum + a[i] - a[i + 1];
      }
    }
    return sum;
  };
  auto make_equal = [&](vector<int>& a, int dif) {
    if (!dif) return -1;
    int sum = 0;
    for (int i = 0; i < n; i += 2) {
      if (a[i] + a[i + 1] == 1) {
        sum = sum + a[i] - a[i + 1];
      }
      if (sum == dif) {
        return i;
      }
    }
    return -2;
  };
  int suma = getsum(a);
  int sumb = getsum(b);
  int goal = (suma + sumb) >> 1;
  int rst = -1, red = -1;
  rst = make_equal(a, goal);
  if (rst == -2) {
    red = make_equal(b, goal);
    assert(red > -2);
  }
  vector<int> rt;
  auto push = [&](int x) {
    if (x < 0) return;
    x += 2;
    reverse(a.begin(), a.begin() + x);
    rt.push_back(x);
  };
  push(rst);
  if (red >= 0) reverse(b.begin(), b.begin() + red + 2);
  for (int i = 0; i < n; i += 2) {
    int gx = b[n - i - 2], gy = b[n - i - 1];
    for (int j = i; j < n; j += 2) {
      if (a[j] == gy && a[j + 1] == gx) {
        push(j - 2);
        push(j);
        goto succ;
      }
    }
    assert(false);
  succ:;
  }
  if (red >= 0) rt.push_back(red + 2);
  printf("%d\n", (signed)rt.size());
  for (auto x : rt) printf("%d ", x);
  putchar('\n');
}
int main() {
  scanf("%d", &T);
  while (T--) {
    solve();
  }
  return 0;
}
