EXPRESSING CERTAINTY

The following are some  examples of expressions for showing certainty and doubt.
Certainty:
1. I’m sure about it.
2. I’m quite sure that he told the truth.
3. I’m absolutely sure about the news.
4. I’m no doubt about it.
5. I’m absolutely certain that he told the truth.
6. I’m sure/certain about …..
7. I’ve no doubt about ……
8. I’m sure/certain about …..
9. I’ve no doubt about …… 

Dialogue:

Rachel : You shouldn't have so many late nights.
Dan : No, I don't think it's that. I was in bed so early last night. I didn't event go out.
Rachel : You must have been feeling bad, then.
Dan : I don't go out every night, you know.

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                 ~ Buku Paket Bahasa Inggris halaman 81