TASK DEFINITION: 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').
PROBLEM: Sexual reproduction involves ____ parents, one male and one female.\Question: Choose the right answer from options given a) zero b) two c) nine d) four

SOLUTION: b

PROBLEM: Circles mark the approximate locations of ____ recently discovered solar systems.\Question: Choose the right answer from options given a) four b) no c) zero d) nine

SOLUTION: a

PROBLEM: Carbon atoms occur in ____ different masses, or isotopes.\Question: Choose the right answer from options given a) three b) seven c) five d) ten

SOLUTION:
a