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').

Astronomers fall in ____ classes - professionals and amateurs.\Question: Choose the right answer from options given a) two b) four c) six d) zero
a

Urea cycle requires the coordination of ____ different tissues.\Question: Choose the right answer from options given a) two b) four c) nine d) zero
a

Today there are ____ quite distinct philosophies in fencing.\Question: Choose the right answer from options given a) zero b) no c) three d) two

d