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').

Aridity presents ____ main obstacles to solitary behavior.\Question: Choose the right answer from options given a) no b) three c) two d) five
c

Many tortoises can retract their head, their ____ limbs and tail into the shell for protection.\Question: Choose the right answer from options given a) no b) one c) two d) four
d

Marine fisheries cause changes at ____ levels of organization of biodiversity.\Question: Choose the right answer from options given a) two b) three c) one d) five

b