I think it is C, because if I'm right present principal is something that is happening presently? If so, C would be the answer because they "are doing" the exercises right now in context.
The answer is C because it is very important to know that it must be suited on time unlike the others.
Answer: To provide reasons why he decided to speed up the nation's efforts to be first in space.
Explanation: Here~! <3
Answer:here is your answer see