first有四个词形：adj. adv. n. pron. 这里主要谈adj.和adv.
first adj.
第一的
Example: He was the first student who arrived at the classroom.
adv. 首先
First I fed the baby. Then I made myself a sandwich.
at first是一个
在句中充当状语
首先
At first I was nervous, but I soon started to relax.
补充一个firstly 修饰句子的副词 首先
The plan was not practical, firstly because of the cost, and secondly because local people did not support it.
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