“please be very quiet”这句话中,为什么要用“be”呢?

“please be very quiet”这句话中,为什么要用“be”呢? so please be very quiet 中的be为什么这么用? please be very quiet为什么be动词不改变 Please be quiet!The other ( ) hear very! so please be very quiet 的意思 but she's very shy.so please be very quiet. please be quiet.变否定句.为什么? Please be quiet 是什么意思? Billy,please be quiet. And please be quiet. Please be quiet Please be quiet.