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: Ocular dryness responds to the use of artificial tears applied every ____ to three hours.\Question: Choose the right answer from options given a) no b) one c) three d) eight
Example Output: b

Example Input: Lung disease is America's number three killer, responsible for ____ in seven deaths.\Question: Choose the right answer from options given a) five b) nine c) one d) four
Example Output: c

Example Input: Most people have ____ problems with nasal prongs.\Question: Choose the right answer from options given a) four b) no c) five d) ten
Example Output:
b