有同學問了一個關於“It's time句型”的問題，如下圖所示：
If you have really been studying English for so long, it's about time you _____ able to write letters in English.
A. should be B. were C. must be D. are
問：我選了A，錯了，答案是B，請問A和B兩個選項區別在哪？
答： 請先參考下面例句：
1.It's time that we get back to some core principles that united Republicans in the past.
NPR: Sen. Ensign: Economy Hurt GOP Candidates
2.So I think it's time that the people know what they've been up to.
FORBES: Intelligent Investing
3.So we've heard conflicting evidence, conflicting statements, and it's time that we get to the bottom of it.
NPR: Political Corner: Gonzales
你給的例句中從句是真實條件從句，主句應該是真實結果主句，那麼正確的答案應該是D。
如果結果主句是虛擬語氣，那麼條件從句應該改為非真實條件句，那麼條件從句就應該用虛擬語氣： if you had really been studying......，那麼較為合適的答案應該選擇B。
通過以上分析，我們可以看出It is time這種句型後面既可以接虛擬語氣，也可以接真實語氣，這點和我們中文是一致的。
如：
1. It is high time that someone gives him the punishment he deserves!
早該有人給他應得的懲罰了。
2. it is time that we gave them a chance.
是我們給他們一個機會的時候了。
最後總結， It is time句型既可以表達虛擬，也可以表達真實，用過去形態表達虛擬，用現在形態表達真實。
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