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').

Ex Input:
Mechanical digestion occurs as ____ strong layers of muscle contract to produce a churning motion.\Question: Choose the right answer from options given a) four b) no c) three d) six

Ex Output:
c


Ex Input:
Cleavage occurs typically in either one, two, three, four, or ____ directions.\Question: Choose the right answer from options given a) six b) three c) ten d) two

Ex Output:
a


Ex Input:
Conservation of momentum Consider ____ interacting objects.\Question: Choose the right answer from options given a) no b) four c) two d) ten

Ex Output:

c