rhinocerises horns lml

metallicafan wrote: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 -- visit and see unnecessarily made parallel here. their antecedent not clear.POE

(B) whether tourists will continue to visit game parks to see one once their horns are --SV error one- their. POE
(C) whether tourists will continue to visit game parks to see rhinoceroses once the animals’ horns have been -- animal's have been perfect tense usage is correct. Hold.

(D) if tourists will continue to visit game parks and see rhinoceroses once the animals’ horns are -- are usage tense change; visit and see parallelism wrong. POE.

(E) if tourists will continue to visit game parks to see one after the animals’ horns have been -- usage of one makes SV error with antecedent rhinoceroses. POE.

What is the meaning when we use "are" instead of "have been" in this question?, Why "have been" is better in this case? -- perfect tense usage since the horns have already been trimmed.(see my usage of perfect tense in the sentence too.)

OA is C