Given a sentence with a missing word, pick the answer option that best fills out the missing word in the sentence. Indicate each answer with its index ('a', 'b', 'c', 'd').

Let me give you an example: Female snakes incubate eggs inside of their bodies, giving birth to live young of ____ or more. \Question: Choose the right answer from the options given a) five b) zero c) seven d) ten
The answer to this example can be: d
Here is why: Snakes give birth to minimum ten young ones so ten is a correct answer.

OK. solve this:
Proprioceptive stimulation has ____ sources.\Question: Choose the right answer from options given a) three b) eight c) two d) six
Answer:
c