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]: Psychiatrists say that one in ____ people are mentally ill.\Question: Choose the right answer from options given a) one b) two c) four d) nine
[A]: c


[Q]: Butterflies have ____ stages in their life cycle.\Question: Choose the right answer from options given a) two b) four c) no d) eight
[A]: b


[Q]: Plankton has ____ known ancestors.\Question: Choose the right answer from options given a) no b) two c) seven d) ten
[A]:
b