Please help me out- ;-;

A right triangle has legs of lengths a and b, and hypotenuse of length c. According to the Pythagorean Theorem, which of the following is true?

A.) (a + b)^2 = c^2
B.) a^2 – b^2= c^2
C.) a^2 + b^2= c^2
D.) a^2 = b^2 + c^2