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').

[Q]: Black widows mature in ____ to four months.\Question: Choose the right answer from options given a) two b) seven c) eight d) zero
[A]: a


[Q]: Avian kidneys have ____ kinds of nephrons.\Question: Choose the right answer from options given a) four b) eight c) no d) two
[A]: d


[Q]: Sexual maturity takes ____ years.\Question: Choose the right answer from options given a) two b) three c) four d) eight
[A]:
a