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').

Food chains consist of ____ trophic levels.\Question: Choose the right answer from options given a) ten b) three c) one d) four
d

Songbirds have ____ sets of vocal chords.\Question: Choose the right answer from options given a) six b) two c) eight d) ten
b

Spiders have eight legs and usually have ____ eyes.\Question: Choose the right answer from options given a) one b) eight c) zero d) six

b