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').

Ex Input:
Poles CAN occur at ____ frequency.\Question: Choose the right answer from options given a) six b) four c) zero d) eight

Ex Output:
c


Ex Input:
Vaccinated newborns have protection for at least ____ years.\Question: Choose the right answer from options given a) four b) five c) two d) no

Ex Output:
b


Ex Input:
Light stimulation activates ____ outward currents.\Question: Choose the right answer from options given a) ten b) four c) six d) two

Ex Output:

d