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

Dogs are pack animals, and ____ dogs is the minimum number for proper socialization.\Question: Choose the right answer from options given a) four b) five c) no d) zero
b

Mangroves have ____ basic organs lika any other ordinary plant, the stem, the leaf and the root.\Question: Choose the right answer from options given a) no b) nine c) one d) three

d