Since an elephant that has no tusk is worthless to poachers, the Wildlife Protection Committee plans to protect selected elephants from being killed by poachers by cutting off the elephants’ tusks.
The Wildlife Protection Committee’s plan assumes that
(A) poachers do not kill elephants that are worthless to them
(B) tuskless elephants pose less of a threat to humans, including poachers, than do elephants that have tusks
(C) tuskless elephants can successfully defend their young against nonhuman predators
(D) elephants are the only animals poachers kill for their tusks
(E) imposing more stringent penalties on poachers will not decrease the number of elephants killed by poachers
When the question asks you what the assumption is, you have to select an answer choice that if negated, the whole argument or conclusion falls apart.
That happens if you negate A. If poachers kill worthless elephants, then the whole plan of the WPC makes no sense.
You can continue checking other options just to make sure, even though A is quite eloquent.
B, C, and D are not directly related to the subject matter.
E is may confuse you, but is not so strong and clear as A. If more stringent penalties 'decrease' the number of elephants killed, anyways can't be compared to the plan of the WPC of stopping definitely all kills.