Choose the option that best fills in the sentence:
It is becoming ______ to find a job.

In the sentence, it's said that it's becoming difficult for him to find a job.
That means that he's been trying and he compares every day it's becoming more difficult.
'harder' is the comparative degree of 'hard'.
So, 'harder and harder' is the correct solution.
So the correct solution is, It is becoming harder and harder to find a job.