be 吾明喔

先看另一例句：
The boy is believed to have stolen the pen.
to 之後的have stolen應該明啦
The boy is believed to (be wearing) a white pullover and blue jens
其實 ( ) 中應是am wearing. 那男孩正穿著一件白色-------
但 am 字會隨著主詞而變成are, is
不過在to 之後就統一用be (是verb to be) 的be
因此，is,am,are稱為verb to be

其實你不要單單看be字，應該看be wearing；be wearing 是進行式，正如我們說he was watching TV when I visited him. 所以be wearing也是用進行式，這句的意思是，那男孩相信當時正穿著白色套衫和藍色牛仔褲