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]: Embryos develop and hatch in about four weeks, then spend four to ____ months in the tadpole stage.\Question: Choose the right answer from options given a) five b) nine c) eight d) two
[EX A]: a

[EX Q]: Spores have ____ combinations of sexes.\Question: Choose the right answer from options given a) four b) five c) seven d) three
[EX A]: a

[EX Q]: Volcanoes emit ____ sorts of ozone-depleting compounds.\Question: Choose the right answer from options given a) eight b) ten c) six d) two
[EX A]:
d