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').

Many scientists believe the neutrino has ____ mass at all.\Question: Choose the right answer from options given a) eight b) zero c) two d) no
d

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
a

Opposite rays are ____ collinear rays with the same endpoint.\Question: Choose the right answer from options given a) four b) eight c) zero d) two

d