To prove that the sum \( t = r + s \) is irrational when \( r \) is a rational number and \( s \) is an irrational number, the correct sequence of steps would be:
- Step 2: For a contradiction, assume that \( t \) is rational, and write \( r \) and \( t \) as fractions.
- Step 1: Subtract, writing \( s \) as a fraction.
- Step 4: Find a common denominator.
- Step 3: Realize a contradiction.
Thus, the answer would be: Step 2, Step 1, Step 4, Step 3.
In the provided options, the closest match to that order is:
Step 2, Step 4, Step 1, Step 3 (though note that Step 4 should logically follow Step 1, but this is the best available option).
So, the answer is: Step 2, Step 4, Step 1, Step 3.