是狀語從句還是賓語從句

請看下面一道題：I don’t know if he _________ tomorrow.
A. come                B. comes               C. will come             D. is coming
【分析】此題容易誤選B。認爲 if 引導的是條件狀語從句，從句謂語要用一般現在時表示將來意義。其實，此題應選C，句中if引導的不是條件狀語從句(即if≠如果)，而是賓語從句(即if＝是否)，句意爲“我不知道明天他是否會來。，句意爲”請看以下類似試題：

(1) I don't know if she _________, but if she _________ I will let you know.
A. comes, comes                               B. will come, will come
C. comes, will come                      D. will come, comes
答案選 D，第一個 if 引導的是賓語從句，第二個 if 引導的是條件狀語從句。

(2) “When _________ he come?” “I don’t know, but when he _________, I’ll tell you.”
A. does, comes                                 B. will, will come
C. does, will come                             D. will, comes
答案選 D，第一個 when 疑問副詞，用於引出一個特殊疑問句；第二個 when when 是從屬連詞，用於引導時間狀語從句。

(3) “When he _________ is not known yet.” “But when he _________, he will be warmly welcomed.”A. comes, comes                              B. will come, will come
C. comes, will come                         D. will come, comes
答案選 D，第一個 when 引導的是主語從句，第二個 when引導的是時間狀語從句。