[問題]OG(11th) 63

[ergh]

63. 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

ans:C

我有以下問題：
1.og 的解釋說when only two alternatives are possible,whether(or whether or not) is properly used rather than if，這樣是說在考試時，當碰到"是否"的意思時，都要選whether嗎？這樣的理論為何？還是我搞錯意思？

2.我不太瞭解為何 once後要加現完式?
還麻煩幫忙解說一下，謝謝

[lrainy]

應該是因為whether帶出名詞子句 而if帶出副詞子句
至於once的用法...希望有人解答

[hccill]

還請各位大大參考~
1.應該是(1)當if為"如果"時,是副詞子句,修飾主要子句的動詞
(2)當if為"是否"時,等同於whether,是名詞子句,可當主詞或受詞
在此,ETS的解釋是說,當有兩樣東西,要表"是否"時(例如:是否為A或B),最好用whether而不要用if,因為我也不是native speaker,這中間的差異,或為何要這樣用,
我也不是很了解,不過在OG,Ov裡,你可以發現,正確答案幾乎都是用whether,而不是用if

2.根據Longman Dictionary
(1)once為Adv時,翻譯為"曾經":
at some time in the past, but not now;in the past, at a time that is not stated

Ex:I once ran 21 miles.

(2)once為conj.時,翻譯為"一旦"
from the time when something happens
=>用現在完成式較佳
所以,once the animals' horns have been trimmed這句話可以翻譯為:
"ㄧ旦動物們的角被修剪之後"

open to discuss~