▲你的理解是错误的。在 He was among the first to arrive 中：

1. 代词 he 用作主语。

2. was 为系动词。

3. 介词短语 among the first to arrive 用作表语。在这个表语中，the first 为介词 among 的宾语，不定式 to arrive 为修饰 the first 的定语。

▲如果 the first 紧跟在系动词 be 之后，则为表语。如：

He was the first to come. 他是第一个到的。

She was the first to arrive. 她是第一个到达的。

You will be the first to speak. 你将第一个发言。

Which of the runners was the first to cross the finish line? 哪一个赛跑运动员首先过终点线？

I was the first to arrive at the inn and got the pick of rooms. 我第一个到达旅馆，所以可以任意挑选房间。

The Blacks were the first to be fired and the last to be hired.最先被解雇是黑人，最后被雇用的也是黑人。