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').

Female elephants have babies about ____ years apart, and they have only one each time.\Question: Choose the right answer from options given a) eight b) one c) zero d) three
d

Big bluestem grows up to ____ feet tall.\Question: Choose the right answer from options given a) seven b) no c) nine d) eight
c

Green lines represent the boundaries between the ____ hemispheres.\Question: Choose the right answer from options given a) two b) five c) seven d) four

a