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: Giraffes sleep less than ____ hours a day.\Question: Choose the right answer from options given a) two b) six c) seven d) ten
Example Output: a

Example Input: Statistics show that within ____ years of divorce, many people marry a second time.\Question: Choose the right answer from options given a) four b) nine c) six d) three
Example Output: d

Example Input: Gene therapy is a very young science that has been used in patients for only about ____ years.\Question: Choose the right answer from options given a) five b) one c) ten d) no
Example Output:
c