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').

Some experts believe whining peaks around the ages of ____ or four.\Question: Choose the right answer from options given a) three b) no c) four d) seven
a

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

Love is a marriage of two hearts and ____ souls.\Question: Choose the right answer from options given a) eight b) nine c) zero d) two

d