The world needs to act fast if we ____in stabilizing climate change and thereby prevent its worst impacts. (C) are to succeed 為什麼答案是(C)?

當"be"作為助動詞時，配合不定式(be to do something)，可用於假設子句(conditional clause type 1)作為目標 aim，而主句則說明要達標之條件。

Type 1 conditional:
IF + simple present (be to do something), simple future / modal / simple present
1. If we are to succeed in ..., the world will need to act fast. (future used in main clause to indicate possibility)
2. If we are to succeed in ..., the world shall need to act fast.  (modal used in main clause to increase certainty)
3. If we are to succeed in ..., the world needs to act fast.  (present used in main clause to indicate factual aspect)

1,此句非假設語氣，即非與事實相反，假設語氣如If I were rich,I would travel the whole world.
2,本句為條件句，前一事件成立，後一事件一定會發生，所以後句用現在式，但為何不直接用succed，是因為區別其後發生之時間序列，
3,不知你答案有無succed選項，所以用猜測的

例如，您仍然喜歡部落衝突，舉個例子嗎？

The world needs to act fast ...
是主句

附以條件性的假設子句
...if we are to succeed in stabilizing climate change ...
因為(C)是正確的文法：


沒有其他選擇。