as 加形容词或副词 加as 那副词是不是要变为原级?形容词要不要变为什么?还有这个短语的用法?

as ...as ...“和...一样”
在两个as中间必须加原级,无论是形容词还是副词,都得用原级.
如 He is as tall as I.
He runs as fast as I
当这个句型用于否定句时,第一个as可以写成so
如 He isn't as tall as I.= He isn't so tall as I.
He doesn't run as fast as I.= He doesn't run so fast as I.