一道SAT语法题麻烦会的盆友解答一下,to be elected在句子里是什么成分呢?：

一道SAT语法题麻烦会的盆友解答一下,to be elected在句子里是什么成分呢?：
the first Asian American to be elected givernor in the United Sates,George Ariyoshi of Hawaii has served longer ahtn any of his predecessors when he retired from office in 1986.这里想问问to be elected在句子里起什么成分呢?为什么能用在过去式里?
还是不了解，为什么这里不能用the first Asian American elected givernork,为什么要用to be呢？只是强调是第一个吗？还是有其他原因？