Could someone tell me the answer of that?

[Zackscofieldoconner]

What's the usage of must have and must have been?
and what's the usages of can have?
and i would prefer it in sentence

[Dozy]

Here are some uses that come to mind:

1. "must have + past participle" expresses the belief that something happened, or the belief that something was the case, based on the available evidence. For example:

"The keys aren't here. Someone must have taken them." (Because they aren't here, you assume that someone took them.)

2. "must have been" is a special case of this, where the verb happens to be "be":

"It must have been terrible when your sister died." (You assume/believe that it was terrible, based on what you have been told, your general understanding of such situations, etc.)

3. Additionally, "must have been + past participle" is used to make passive forms:

"The keys aren't here. They must have been taken by someone."

4. When not followed by a past participle (i.e. with "have" as the main verb), "must have" expresses the belief that someone or something has something (in any sense of "has"):

"The keys aren't in my pocket. You must have them." (You believe that the other person has them.)

5. "must have" can also be used to urge someone to do something, or to state that one greatly desires something:

"You must have one of these cakes! They're delicious."
"I must have one of these new iPads!"

[Beeesneees]