A proposal has been made to trim the horns from rhinoceroses to discourage poachers; the question is whether tourists will continue to visit game parks and see rhinoceroses after their horns are trimmed.

A) whether tourists will continue to visit game parks and see rhinoceroses after their horns are
B) whether tourists will continue to visit game parks to see one once their horns are
C) whether tourists will continue to visit game parks to see rhinoceroses once the animals' horns have been
D) if tourists will continue to visit game parks and see rhinoceroses once the animals' horns are
E) if tourists will continue to visit game parks to see one after the animals' horns have been

[spoiler]OA: C[/spoiler]

OG mentions that the correct verb form should be present perfect, i.e. " have been trimmed" because event 1: the trimming of the animal's horns should occur before even 2: tourists arrive.

But why it is not future perfect & future but present perfect & future?

Thanks in advance.