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').

Example Input: Most marine sediments are of ____ basic types.\Question: Choose the right answer from options given a) three b) ten c) two d) nine
Example Output: c

Example Input: Most school aged children pass at least ____ stools per week, with an average of one stool per day.\Question: Choose the right answer from options given a) three b) one c) six d) zero
Example Output: a

Example Input: Water is able to diffuse freely between the ____ cells.\Question: Choose the right answer from options given a) two b) six c) three d) five
Example Output:
a