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:
Reverse osmosis uses ____ to ten gallons of water to produce one gallon of drinking water.\Question: Choose the right answer from options given a) two b) zero c) five d) three

Ex Output:
d


Ex Input:
Ladybugs have ____ legs and keep their wings tucked away until they are ready to fly.\Question: Choose the right answer from options given a) six b) eight c) one d) zero

Ex Output:
a


Ex Input:
Controlled grazing affects riparian areas in ____ ways.\Question: Choose the right answer from options given a) two b) zero c) five d) ten

Ex Output:

a