C
Complementary angles have a sum of 90 degrees. So to solve you would add each angle to the other to see if they add up to 90 degrees.
A. 31 + 69 = 100 (does not equal 90, so no)
B. 90 + 90 = 180 (they equal 180, which would be supplementary)
C. 56 + 34 = 90 (they equal 90, therefore they would be the complimentary angles)