The correct sequence for the proof that the sum \( t = r + s \) is irrational if \( r \) is rational and \( s \) is irrational is:
1. **Step 2**: For a contradiction, assume that \( t \) is rational, and write \( r \) and \( t \) as fractions.
2. **Step 4**: Find a common denominator.
3. **Step 1**: Subtract, writing \( s \) as a fraction.
4. **Step 3**: Realize a contradiction.
So the correct response is:
**Step 2, Step 4, Step 1, Step 3**.