We often use some adverbs in speaking as short responses to show attitude or viewpoint:

You know DVDs? Can you record onto them?

Absolutely.

Dr Kahn is very nice. He’s very interested in his patients.

Oh, do you think so?

Definitely.

There might be a film on at 2 pm that we could watch.

Yeah, probably.

Mandy isn’t going because she just doesn’t like Rick.

Exactly.

Maybe she bought two of the same sweaters in case something happened to one.

Yeah, possibly.

It should be called ‘English Test’ not ‘Test of English’.

Precisely.

We often use not really in this way to soften a no-answer:

Do you not like chocolate?

No, not really.

We use certainly and of course typically as a reply to a request for a service or favour:

Can I have the bill please?

Certainly.

[in a clothes shop]

Is it OK if I try these on?

Of course.

We often use adverbs that make the meaning stronger (very, extremely, really) as a short response:

He’s an intelligent dog, isn’t he?

Yes, very/extremely/highly.

See also:

Discourse markers as responses

Adverbs

Adverbs: types