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]: All mass spectrometers consist of ____ distinct regions.\Question: Choose the right answer from options given a) three b) one c) two d) zero
[EX A]: a

[EX Q]: Teething begins for most babies around ____ to six months.\Question: Choose the right answer from options given a) three b) four c) five d) seven
[EX A]: b

[EX Q]: Essential oils have a non-toxic, residual effect of up to five months from just ____ application.\Question: Choose the right answer from options given a) no b) zero c) two d) one
[EX A]:
d