Suitable habitats for gray wolves have greatly diminished in area. In

why not B ? can anyone explain it to me ?

This is an assumption question. An assumption by definition is an unstated piece of an argument that is necessary/required for the argument to hold good. The stimulus is fairly easy to follow and decomp. The conclusion is the last sentence "Striving to bring back these animals to places where they will only face lethal human hostility is immoral." Now let us look at the options:

(A) an appeal to an authority
The stimulus might seem to be an appeal to an authority. Probably, an animal conservationist is trying to appeal to the government body. However, we are not given any context on this regard. This option is to confuse the test taker. When thought from an assumption perspective, is this an assumption you need to arrive at the conclusion? Clearly no.

(B) a belief that gray wolves are dangerous to human beings and livestock
Is it necessary to believe that gray wolves are dangerous to human beings and livestock to conclude that "Striving to bring back these animals to places where they will only face lethal human hostility is immoral." Let us consider that gray wolves are indeed not dangerous. Does it hurt the conclusion that these animals will only face lethal human hostility and that it is immoral. NO! Hence, this is not a valid assumption

(C) an assumption that two events that occur together must be causally connected
There is no causality here as such. The argument does not depend on any causal relationship

(D) an assumption that the future will be like the past
This is the correct answer. The author of the argument is clearly assuming that the future will be like past meaning gray wolves will be hunted out of existence. Only because the author considers this assumption is the author making the conclusion that "Striving to bring back these animals to places where they will only face lethal human hostility is immoral." Negating this as "An assumption that the future WILL NOT be like the past" will kill the argument and conclusion falls apart.

(E) a threat of violence against those persons presenting the opposing view
This is totally irrelevant to the argument

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