Correct the errors if necessary. 1. Since when are they waiting for us? 2. I have been...

Question

Correct the errors if necessary.

1. Since when are they waiting for us?

2. I have been looking for my passport since I came home.

3. His friends have been having this building for ten years.

4. In recent years, scientists are developing many new machines.

Answer 1

1. Since when have they been waiting for us?
2. I have been looking for my passport since I came home.
3. His friends have had this building for ten years.
4. In recent years, scientists have developed many new machines.