as 與 as 之間 可以放什麼?

as is an adverb for comparison, so between as & as, you should put ADJECTIVE only.

e.g. She is as tall as her father.
e.g. Her skin is as soft as baby's
e.g. He runs as fast as you.

Adjectives and adverbs

adjective
e.g. as fast as /// as slow as