am /is / are + being 是动词 be 的现在进行时形式。例如:
My son is being a good boy today . 今天我儿子很乖。
You are being very patient with her tonight . 今晚你对她真耐心。
Don't talk rot ! I'm being serious . 不要胡说!我是严肃认真的。
I'm not being hard on anybody ! I'm being sensible . 我不是在对谁苛刻,我是在理智行事。(这些例句摘自赵俊英:《现代英语语法》)