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:
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

Ex Output:
a

Ex Input:
Vision disorders affect ____ in every four school-age children.\Question: Choose the right answer from options given a) nine b) one c) five d) six

Ex Output:
b

Ex Input:
Most birds of prey have three toes in front on their feet , and ____ toe in the back.\Question: Choose the right answer from options given a) one b) no c) zero d) six

Ex Output:
a