Question

must have been和must be的区别

要口诀，简短，易懂。

Answer 1

must have been 和 must be的区别在 have
have在这里表示是 动作已经完成。所以
must have been是对过去的事实的肯定猜测
must be是对现在事实的肯定猜测
e.g.
She sings so well.I think she must have been a singer.
她唱得真好。我想她以前肯定是名歌手。
he doesn't come to school today. He must be ill.
他今天没有来上学，肯定是病了。

Answer 2

must be和must have been都表示推测，区别就是must be表示一般将来时和现在完成时的推测，must have been表示过去式的推测，所以我建议大家不要记混

Answer 3

must have been“(过去)肯定是”
must be“肯定/一定是”