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').

Most children improve in three to ____ days.\Question: Choose the right answer from options given a) seven b) six c) four d) ten
a

Statistics show that within ____ years of divorce, many people marry a second time.\Question: Choose the right answer from options given a) four b) nine c) six d) three
d

Astronomers believe that ____ binary star systems they have observed probably contain black holes.\Question: Choose the right answer from options given a) eight b) no c) seven d) six
c