Haro has 17 model cars, 31 model trucks, and 9 model airplanes on the shelf in his room. His sister thought it would be funny to hide all the red models. Now Haro only has 39 models on his shelf. Which number sentence could be used to find how many red models his sister hid?
A. (17 + 31 + 9) – r = 39
B. 17 + 31 + 9 + r = 39
C. (17 + 31 + 9) + r = 39
D. 39 + 17 + 31 + 9 = r