Use the Present Perfect, the Present Perfect Continuous or the Present Continuous.
1. I (wait) for the prices of the houses to come down before buying a house, but I think I (wait) too long and the prices are beginning to go up again.
2. Call the children in! They (play) outside since early morning and (not to do) their homework yet.
3. I'm afraid she (not to finish) typing those letters yet. She (deal) with customers all morning.
4. You (fix) this shelf for an hour. Let's ask Father to help you.
5. The students (translate) the article for 20 minutes but they (not to finish) it yet.