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 Q]: Most birds have ____ toes, three that face forward and one rearward.\Question: Choose the right answer from options given a) two b) ten c) nine d) four
[EX A]: d

[EX Q]: Ascidian tunicates come in ____ main forms.\Question: Choose the right answer from options given a) three b) zero c) four d) eight
[EX A]: a

[EX Q]: Former smokers can completely lower their risk of sudden cardiac death within ____ years of quitting.\Question: Choose the right answer from options given a) zero b) two c) ten d) no
[EX A]:
c