[問題]大全343

[Jen-Cheng]

343.If the new airboat does what it is to be doing—travel at high speeds undeterred by sandbars, crocodile-infested mudflats, or marshy hippo haunts—it could revolutionize transport on the 2,900-mile-long Congo River.
(A) If the new airboat does what it is to be doing
(B) If the new airboat does what it is supposed to do
(C) If it does as the new airboat is supposed to do
(D) Doing what it is the new airboat is supposed to do
(E) Doing what the new airboat is to be doing

Ans:B
我的問題在於，為什麼 "if現在式+ 過去式 (could)"

我所知道的有1.if 現在式+現在式
2.if 過去式+過去式
3.if 現在+未來
4.if had+p.p.+ would have p.p.
這題的答案全都是現在式，為什麼？是什麼情況下可以這樣用？

[Jen-Cheng]

頂一下，有人知道嗎？

[Philosophia]

這回答好像有點久～不過，謝謝你又讓我 review 一次 conditional～

這題看起來是 zero conditional
但因為 A 並不永遠等於 B，A 之中有前題，所以 B 之中為了表示 possibility，因而改用了 modal 中的 could.

這題的考點好像不在這裏．我只是挑了一個看起來比較順眼的 B...