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 have a vocabulary of eight to ____ words, including names, by eighteen months of age.\Question: Choose the right answer from options given a) ten b) one c) seven d) eight
a

Influenza epidemics are ____ times more likely during solar maxima.\Question: Choose the right answer from options given a) ten b) eight c) no d) four
d

Quaternions have ____ imaginary axes, which creates the factor of three.\Question: Choose the right answer from options given a) ten b) one c) eight d) three

d