Answer:
C. 89,90 and 91.
Explanation:
Since the loop condition is grade>= 90 the values i would use to test the loop are 89,90 and 91.
So that we can check for 3 different conditions.
89 is less than 90 so we can check for <90.
90 is equal to 90 so we can check for =90.
91 is greater than 90 that condition will also be checked.
Hence we conclude that the answer is option C.