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: Neutrinos are particles with almost ____ mass and no electric charge.\Question: Choose the right answer from options given a) no b) two c) zero d) five
Example Output: a

Example Input: Studies show that childhood obesity is epidemic and that ____ in five children is overweight.\Question: Choose the right answer from options given a) one b) two c) nine d) ten
Example Output: a

Example Input: Chronic insomnia lasts longer than ____ months and often needs to be treated.\Question: Choose the right answer from options given a) three b) eight c) no d) seven
Example Output:
a