1.By 1980, they will have to produce at least 20 milion barrels of oil
a day if the West ______.
A.is to avoid a crippling energy crisis
B.avoids a crippling energy crisis
ANS:A
想請問為什麼不能用B呢？兩者的差別在哪裡呢？
2.I could not finish the homework ____.
A.by he had come
B.until he has come
c.when he comes
D.before he came
ANS:D
這題想請問為什麼不能使用A～
謝謝板上英文高手的解答！！
關於時式的用法好混亂還請大家不吝賜教！

2 by是介系詞不能加句子1是與未來事實相反的假設

be to V用法這板有討論過 /be to V 搜題目一樣的文章是說這用法真是百考不膩...

這跟假設語氣無關。