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: Mosquitoes have ____ distinctive life stages, with the first three stages being spent in the water.\Question: Choose the right answer from options given a) four b) zero c) nine d) five
Example Output: a

Example Input: Alleles segregate independently yielding ____ possible allelic combinations in gametes.\Question: Choose the right answer from options given a) ten b) one c) four d) nine
Example Output: c

Example Input: Caffeine has a purine ring in which each of ____ nitrogen atoms bears a methyl group.\Question: Choose the right answer from options given a) zero b) four c) no d) three
Example Output:
d