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]: Female bilbies have a backward-opening pouch with ____ nipples.\Question: Choose the right answer from options given a) no b) two c) five d) eight
[A]: d


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


[Q]: Leeches die after ____ or two bouts of reproduction.\Question: Choose the right answer from options given a) four b) one c) ten d) five
[A]:
b