[問題]OG(11th)94

[Jacklin]

The Coast Guard is conducting tests to see whether pigeons can be trained to help find survivors of wrecks at sea.
(A)to see whether pigeons can be trained to help find
(B)to see whether pigeons can be trained as help to find
(C)to see if pigeons can be trained for helping to find
(D)that see if pigeons are able to be trained in helping to find
(E)that see whether pigeons are able to be trained for help in finding
正確答案:(A)
我的問題是，解釋裡說到(D)"are able to" should be replaced by the concise "can" ，除了can較簡潔外，兩者意思一樣在任何情況下是可以互換的嗎？
煩請指導～

[evelyn_yeh]

can 和 be able to 在被動句型中較有差異
be able to 表能力 capable of 表屬性, can表狀況
pigeons can be trained 是說p可以被人trained
pigeons are able to be trained 是說p 本身具有被train的能力
舉一個更明顯的粒子
pollution can be removed // pollution is able to be removed
要選擇用can 或 be able to 除了要看主詞以外,還要看動作
be able to --'通常' 主詞是具有表現能力的生物,而動作是此生物本身有意志可主宰的
dog is able to run at a very fast speed(當然要用can也可)
table can be cleaned.(這就不能用able to )