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]: Parapsychologists have ____ basic approaches to their subject matter.\Question: Choose the right answer from options given a) three b) two c) ten d) five
[A]: b


[Q]: Background radiation comes from ____ sources.\Question: Choose the right answer from options given a) zero b) three c) four d) no
[A]: b


[Q]: Snakes have either a three-or ____ chambered heart.\Question: Choose the right answer from options given a) four b) two c) nine d) one
[A]:
a