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').

Ex Input:
Condors become sexually mature at about five or ____ years of age and mate for life.\Question: Choose the right answer from options given a) nine b) seven c) one d) six

Ex Output:
d

Ex Input:
Most volcanoes erupt for ____ to four weeks and then rest.\Question: Choose the right answer from options given a) three b) four c) one d) eight

Ex Output:
a

Ex Input:
Male robins are well known for dive-bombing people and predators within ____ feet of a nest.\Question: Choose the right answer from options given a) one b) ten c) nine d) two

Ex Output:
b