系动词有哪些？
5.1 be动词类：am; is; are; was; were；
5.2 感官动词类：look“看起来”；seem“看起来”；sound“听起来”；smell“闻起来”；taste“尝起来”；feel“摸起来，觉得，感到”；感官动词的汉语意思中带有“……起来”；
（注意和行为动词的区别：look“看，瞧”；smell“闻，嗅”；taste“尝，试吃”；feel“摸”）
5.3 含有“变成，变”意思的系动词：become“变成”；turn“变成”get“变得，变成”等；
5.4 含有“保持”意思的系动词：remain“保持”；stay“保持”；keep“保持”等；
（stay“待在”, keep“保留，保存”等表示其他意思，就不再是系动词了）
【知识点】为什么是主系表句而不是主谓宾句？
主语 系动词 表语
He became a doctor in 1988.（主系表句）
He joined the hospital in 1988.（主谓宾句）
连系动词不可以带宾语，因为连系动词不是及物动词，比如我们把become（变成）带入及物动词检验结构中：
“我become（变成）它，它被我become（变成）”，意思表达不通顺，中国人都不会这样讲，所以become（变成）不是及物动词；那么a doctor不是宾语，它是什么句子成分呢？在系动词后面的名词在语法上叫“表语”，因为它说明主语的情况而使句子意思完整。表语可以是形容词、名词、代词、介词短语、名词性从句等。
6. 表语有哪些种类？
表语可以是形容词、名词、代词、介词短语、名词性从句等
6.1形容词做表语
(1) Each of us feel a little bit tired, so we were happy because we had done a good deed.
（解析：形容词tired做feel的表语，happy做were的表语，根据前后一致原则feel改为felt, 根据逻辑关系so改为but，全句修改为：Each of us felt a little bit tired, but we were happybecause we had done a good deed.）
(2) I feel uneasily recently.
（解析：副词不能做表语，应改为：I feel uneasy recently.）
(3) It’s always difficult to communicate.
（解析：To communicate is always difficult. 表语difficult来说明主语to communicate的情况，使句子意思完整）
(4) I felt excited by the amazed beauty of nature.
（解析：excited做felt的表语，amazed“ed表示感到…的，修饰人”， amazing“ing表示令人…的，修饰物”，句子应改为：I felt excited by the amazing beauty of nature.）
(5) I am so exciting that you will come to China.
（解析：应改为：I am so excited that you will come to China.）
(6) I was really disappointing and about to leave when he walked out a building．
（解析：was后面有两个表语：disappointed和about to leave，应改为：I was reallydisappointed and about to leave when he walked out a building．）
(7) The experience was very interested.
（解析：应改为：The experience was very interesting.）
(8) The assistant was clearly as embarrassing as my sister; for I just thought it was funny!
（解析：应改为：The assistant was clearly as embarrassed as my sister）
(9) She was, in fact, rather attractively.
（解析：插入语in fact先忽略，She was rather attractively.句子中系动词was后没有表语，副词不能做表语，应改为：She was, in fact, rather attractive.）
(10) They are silently, and it was clearly that things were not going well.
（解析：副词不能做表语，应改为：They are silent, and it was clear that things were not going well.）
(11) Everyone else seems very nice and warmly here.
（解析：系动词seem后面两个表语nice和warm, 应改为Everyone else seems very nice andwarm here.）
(12) My friend Nick told me story about his experience back in the US, which was veryinterested.
（解析：which指代整个句子所表达的事情，故不能用interested, 应改为：My friend Nick told me a story about his experience back in the US, which was very interesting.）
(13) As you are very popularly with us Chinese high school students, we’d like to invite for you to the exhibition.
（解析：副词不能做表语，for去掉，应改为：As you are very popularly with us Chinese high school students, we’d like to invite you to the exhibition.）
6.2 名词做表语
(1) I am a boy in the first grades of a senior high school.
（解析：名词a boy做表语，grade用单数，应改为：I am a boy in the first grade of a senior high school.）
(2) This is a good chance to learn Chinese Kong Fu．
（解析：a good chance to learn Chinese Kong Fu做表语，体会一下前定语good和后定语to learn Chinese Kong Fu, 长定语一般后置）
(3) It was unforgettable trip.
（解析：应改为：It was an unforgettable trip.）
(4) Christine was just a girl in one of my classes.
(5) One day I saw a second-hand bicycle, that was only one hundred Yuans.
（解析：非限制性定语从句中连接词不能用that, 人民币和日元Yuan复数不能加s，应改为：One day I saw a second-hand bicycle, which was only one hundred Yuan.）
(6) It was a lesson to us that it was possible give without expect anything in return.
（解析：it was possible give without expect anything in return. 这个简单句中已有谓语动词was,其他动词就是非谓语动词：to do; doing; done，介词without后面跟动词ing，全句应改为：It was a lesson to us that it was possible to give without expecting anything in return.）
(7) I am secretary of the City Student Union (CSU).
（解析：名词secretary后面有后定语修饰表特指，应改为：I am the secretary of the City Student Union (CSU)）
6.3 介词短语做表语
(1) I was the Shanghai Railway Station to buy a ticket to Hangzhou.
（解析：was后面都是表语，说明主语情况的，小地点前应加介词at）
(2) The rate remained above the previous level.
（解析：remained后面介词短语是表语）
(3) When I was in high school, most of my friend had bicycles.
（解析：in high school是表语，most of后面要跟复数，friend改为friends）
(4) More than 1000 paining will be on show.
（解析：介词短语on show是表语，根据前后一致painting改为paintings）
6.4 从句做表语（表语从句）
(1) The chances are that you can perform the task.
(2) The point is that you have to keep your promise to help her with her English.
(3) The fact is that, with the new guided system, flying will be safer than ever.
(4) The problem is that I forget her phone number.
（解析：这些从句都做系动词的必要，用来说明主语情况，使句子意思完整）
7. 注意几个问题
7.1 stay, turn, keep, feel
7.2 不要看到be动词就是主系表句
I was playing at my cousin house.
