What is the definition of complimentary angles?

Two angles that add to be 180°

Two angles that have a difference of 90°

Two angles add to be 90°

Two angles that have a difference of 180°

Simple, the answer to this is ...

two angles that add up to be the sum of 90°

Now, a quick tip.

To know the difference between supplementary (180°) and complementary (90°) angles ...

the s in supplementary can be viewed as an 8, while in complementary the c can be viewed as a 9 ...

Thus, your answer ... C.