45. ________ the movie was so boring, I doubt I would have gone to see it.
(A) I had known if
(B) If I knew
(C) If had I known
(D) Had I known

這題的正確答案是 (D) Had I known。

文法解說：

這題考的是「與過去事實相反的假設語氣」中的「倒裝句」（Inversion）。

1. 判斷假設語氣類型：

   • 首先看主要子句： ...I doubt I **would have gone** to see it.

   • would have + 過去分詞 (gone) 這個結構是「第三類條件句」（Third Conditional）的典型特徵，用來描述與過去事實相反的假設結果。

   • 這句話的實際情況是：我不知道電影很無聊，（可能）去看了。假設的情況是：如果我早知道，我大概就不會去了。

2. 第三類條件句的標準結構：

   • If + 主詞 + had + 過去分詞, ... 主詞 + would have + 過去分詞.

   • 按照這個標準結構，這句話應該是： **If I had known** the movie was so boring, I doubt I would have gone to see it.

3. 倒裝句的形成：

   • 在正式或書面語中，假設語氣的 if 子句可以省略 if，然後將助動詞 had 移到主詞 I 的前面，形成倒裝句。

   • If I had known... -> **Had I known...**

   • 這種倒裝結構的意思和用法與原本的 if 子句完全相同。

選項分析：

• (A) I had known if: 語法結構完全錯誤。

• (B) If I knew: 這是「第二類條件句」的 if 子句（If + 過去式），用來描述與現在或未來事實相反的假設。但主要子句 would have gone 是第三類的，兩者時態不匹配。

• (C) If had I known: 這是錯誤的結構，把 if 和倒裝句混在一起了。只能擇一使用，不能並存。

• (D) Had I known: 這是 If I had known 正確的倒裝形式，完全符合第三類條件句的文法。

結論：

由於主要子句使用了 would have gone，條件子句必須使用與過去事實相反的假設語氣。Had I known 是 If I had known 的正確倒裝形式。

整句話的意思是：「要是我早知道這部電影這麼無聊，我大概就不會去看了。」

1️⃣ 把完整原句還原成「正常順序」

題目是：

________ the movie was so boring, I doubt I would have gone to see it.

正確填法其實是這句的「倒裝版」：

If I had known the movie was so boring, I doubt I would have gone to see it.

中文：

如果我早知道這部電影那麼無聊，我懷疑我會不會去看。
（= 應該就不會去了）

這是典型的「與過去事實相反的假設」：

• If + 主詞 + had + p.p.（If I had known…）

• 主句：would have + p.p.（would have gone）

2️⃣ 為什麼會變成 Had I known？

英文裡有一個「假設語氣的倒裝」用法：
當 if 省略時，可以把 had / were / should 提到句首：

• If I had known, I would have…
  ➜ Had I known, I would have…

• If I were you, I would…
  ➜ Were I you, I would…

• If you should need help, call me.
  ➜ Should you need help, call me.

? 所以：

If I had known the movie was so boring…
=
Had I known the movie was so boring…

只是語氣稍微正式一點、書面一點，但意思完全一樣。