1. 表语：
(1) 定义：句子中系动词后面所接的那个部分；
(2)系动词：分为be动词，后面能解形容词的感官动词及相当于be动词用法的实义动词。
①be动词：am/is/are/was/were等；
②后面接形容词的感官动词：feel/sound/look/taste/smell等；
③相当于be动词用法的实义动词：become/keep/remain等。
e.g. Tom is a good doctor.
They are friendly.
That sounds great.
We should keep quiet in the classroom.
2. doing作表语的用法：
(1)表示主语的内容，可以转换到句首作主语；
e.g.Teaching English is my job.
＝My job is teaching English.
(2)表示主语具有的特征、性质和状态(动词ing形式相当于一个形容词)，常译作“令人……的”。
①常用来作表语的现在分词有astonishing，amusing，confusing，disappointing，boring，encouraging，inspiring，moving，tiring，interesting，surprising等；
②这类以-ing结尾的形容词的主语通常为物。
e.g.The problem is quite puzzling.
The music they are playing sounds so boring．
His concern for his mother is touching．
3.动词-ing的转不按规则：
(1)一般情况下，直接加-ing;
e.g. go—going
ask —asking
look—looking
carry—carrying
(2)以不发音的e结尾的动词，去e加-ing;
e.g. write—writing
make—making
take—taking
move—moving
live—living
leave—leaving
(3)以重读闭音节（一个元音加一个辅音）结尾的动词，末尾只有一个辅音字母，双写这个辅音字母，再加-ing；
e.g. get—getting
sit—sitting
put—putting
run—running
begin—beginning
plan—planning
cut—cutting
get—getting
beg—begging
(4)注意（特殊）：
die—dying
lie—lying
tie—tying
picnic—picnicking
panic—panicking
listen—listening
develop—developing
