要说两个东西在某方面一样，就把描述的词放在两个 as 中间：as + 单词 + as。这个单词要用原形，不加 -er。
as + 单词 + as
Amina is as tall as Lars.
This book is as interesting as that one.
Hiroshi runs as fast as his brother.
My bag is as heavy as yours.
Not "Amina is as taller as Lars." — say "Amina is as tall as Lars.". 在 as ... as 中间，单词要用原形：as tall as，不是 "as taller as"。
试一试: Hiroshi runs ___ his brother. (as fast as / as faster as / as fast than) 答案: as fast as — 中间的单词要用原形：as fast as（不是 "as faster as"）。两边都用 as，所以第二个也是 as，不是 "than"：as fast as his brother。
not as ... as
要说一个东西比另一个差一些，加上 not：not as + 单词 + as。
She is not as tall as her sister. (= shorter)
Today isn't as cold as yesterday. (= warmer)
This café isn't as busy as the one downtown.
试一试: Today isn't ___ yesterday. It's warmer. (as cold as / as colder as / as cold than) 答案: as cold as — 还是用 as ... as 这个结构，只是加了 not（"isn't"）：isn't as cold as yesterday。单词还是原形（不是 "colder"），两边都用 as，所以第二个也是 as，不是 "than"。
用 as ... as，还是 -er than？
选之前先问自己：两者一样，还是一个更多？一样 → as + 原级词 + as。一个更多 → -er / more ... than。一个更少 → not as ... as。
The same: Amina is as tall as Lars. (they measure the same)
One is more: Amina is taller than Lars.
One is less: Amina is not as tall as Lars. (= she is shorter)
Watch the word: it stays plain inside as ... as (as tall as), but takes -er with than (taller than).
Not "Amina is as tall than Lars." — say "Amina is as tall as Lars. / Amina is taller than Lars.". as 配 as，-er 配 than。不要把两者混在一起。
试一试: Mei 和 Sofia 都正好 1.65 米高。谁也不比谁高。 哪一句适合两个一样高的人？ (Mei is as tall as Sofia. / Mei is taller than Sofia.) 答案: Mei is as tall as Sofia. — 两人一样高，所以用 as + 原级词 + as：as tall as。"Taller than" 会表示其中一个更高，但事实并非如此。
试一试: My phone is ___ yours, but it isn't ___ that new one. (as new as … as expensive as / as newer as … as expensive than / as new than … as expensive as) 答案: as new as … as expensive as — 两个空用的是同一个结构：as + 原形单词 + as。所以是 as new as 和 as expensive as。不管是肯定句还是 "isn't" 后面，单词都保持原形，两边都用 as。