need not be和 need not have +过去分词表示“不一定”

It need not be true.这不一定真实｡ (It may be true,or not. )

The man need not be thirty.那人不一定 30岁｡ (He may be thirty, or not. )

A man need not be happy though he is rich.富有的人不一定幸福｡ (may be, or not)

He was there then, but he need not have stolen the money.他当时在那里,但他不一定偷了钱｡ (may have or may not have)

He travelled a lot, but he need not have visited the Great Wall.他旅游到过许多地方,但不一定参观过长城｡ (may have or may not have)