助动词没有独立的语义，主要作用是协助谓语动词表示时态、语态或构成疑问式、否定式等

　　助动词和情态动词的共同特点是需要和其他动词搭配使用才有意义，而且句子的否定式和疑问式都可通过这两类词体现

　　一、have/has (现在完成时), had (过去完成时)

　　这组助动词主要用来构成完成时态，形式为：have /has /had + 过去分词

　　如：I haven't seen you for ages.

　　She had mentioned this before.

　　二、be

　　be本身可作谓语动词，但在进行时中它是助动词，与现在分词搭配使用，缺一不可

　　如：She's watching a football match.

　　He's looking for his favorite pet.

　　此外，be和过去分词搭配构成被动语态

　　如：The vicar was killed in a car accident.

　　三、do/does (一般现在时), did (一般过去时)

　　此组助动词用于构成疑问式或否定式

　　如：He doesn't feel like smoking at the moment.

　　Did you meet the manager this morning?

　　四、will, shall, would

　　此组助动词用于构成将来时

　　如：He won't be able to see you until an hour later.

　　Mary promised she would pay you a visit soon.

　　例题：

　　(1)

　　The colors of a rainbow ---- arranged in the same order.

　　(A) which are always

　　(B) and they are always

　　(C) always

　　(D) are always

　　答案：D

　　解释：空格前是句子的主语，之后是过去分词短语，空格处需要补全句子的谓语，A使原句只有从句无主句；B并列句的前一个分句无谓语；arrange与color是被动关系，C是主动式，可排除；只有D助动词are恰好与arranged构成句子的谓语