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').

Young emus are very vulnerable to disease until they are about ____ months old.\Question: Choose the right answer from options given a) no b) ten c) six d) three
d

Food chains consist of ____ trophic levels.\Question: Choose the right answer from options given a) ten b) three c) one d) four
d

Skin cancers are likely to recur within ____ years after treatment.\Question: Choose the right answer from options given a) five b) zero c) three d) no
c