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: Paleontologists specialize in ____ main areas.\Question: Choose the right answer from options given a) eight b) five c) no d) six
Example Output: b

Example Input: Most children improve in three to ____ days.\Question: Choose the right answer from options given a) seven b) six c) four d) ten
Example Output: a

Example Input: Geckos have small round bodies, with ____ pairs of legs.\Question: Choose the right answer from options given a) eight b) six c) ten d) two
Example Output:
d