Complete the sentences with the correct preposition.
- You should keep ………… your voice, so that the teacher won't hear you.
- Let's just keep ………… the subject, we don't have much time.
- I don't have the Internet or TV, so it's difficult to keep ………… ………… the lastest news.
- Don't get discouraged when you fail, just keep ………… trying.
Key
- down
- to
- up with
- on