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').

Youth unemployment is ____ times the adult level.\Question: Choose the right answer from options given a) one b) three c) seven d) no
b

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

Plants are reproductively mature at ____ years of age.\Question: Choose the right answer from options given a) zero b) four c) three d) ten

c