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]: Bone marrow replenishes itself fully within ____ weeks.\Question: Choose the right answer from options given a) nine b) no c) one d) two
[EX A]: d

[EX Q]: Fluorescent lamps are roughly ____ times more intense than ordinary lightbulbs.\Question: Choose the right answer from options given a) six b) one c) three d) eight
[EX A]: c

[EX Q]: Many scientists believe that, sometime around ____ billion years ago, simple life arose.\Question: Choose the right answer from options given a) four b) zero c) one d) seven
[EX A]:
a