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').

Ozone is a molecule containing ____ oxygen atoms.\Question: Choose the right answer from options given a) one b) nine c) no d) three
d

Ossification begins up to ____ months before birth.\Question: Choose the right answer from options given a) nine b) seven c) three d) six
b

Japanese archaeologists recognize, in general terms, four prehistoric and ____ historic periods.\Question: Choose the right answer from options given a) seven b) ten c) four d) eight

c