<u>Answer:</u>
The correct answer option is 'then'.
<u>Step-by-step explanation:</u>
The "to prove" part of the information is the 'then' of the "if-then" statement.
For example, we have this problem:
If , then find the value of y.
Here in this problem, we are asked that 'if' the value of x is true then prove it by substituting in the value.