其实这种句型主语就是
主系表结构。就是主语加谓语加主语补足语或叫
表语主语S、
谓语动词V、补语（主语补语Cs，宾语补语Co）
(S + V + Cs)
1． 此句型的 “V” 是
连系动词，“Cs” 是主语补语，或称表语。充当主语补语的有名词、代词、形容词、副词、数词、介词短语、动词 V-ing 形式或 V-ed 形式、不定式及
名词性从句等，如：
My first name is Bill.
Life is colorful.
Seeing is believing.
Our belief is that things will improve.
2． 常见的连系动词有下列几类：
a. 表示“判断”：be；
b. 表示“变得”、“成为”：become, come, go, fall, get, grow, prove, turn 等；
c. 表示“保持着某一状态”：hold, keep, lie, remain, rest, sit, stay 等；
d. 表示“看起来”、“好像”：appear, look, seem 等；
e. 表示“实感”：feel, sound, taste, smell 等。
e.g. She is a teacher and I am a doctor.
Spring comes and all trees turn green.
He stayed awake all night.
You don’t look happy, what's the matter?
Their plan sounds wonderful.