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: Human females have ____ X chromosomes.\Question: Choose the right answer from options given a) two b) six c) one d) eight

A: a
****
Q: Normal cells have ____ copies of each chromosome.\Question: Choose the right answer from options given a) two b) five c) eight d) no

A: a
****
Q: Benzene burns quite well because it's built around rings of ____ carbon atoms.\Question: Choose the right answer from options given a) eight b) no c) six d) zero

A:
c
****