Chuyển các câu sau sang dạng bị động:

1. **The German didn't build this factory during the Second World war.**
- This factory wasn't built by the Germans during the Second World War.

2. **The Greens are going to paint this house and these cars for Christmas.**
- This house and these cars are going to be painted by the Greens for Christmas.

3. **Ann had fed the cats before she went to the cinema.**
- The cats had been fed by Ann before she went to the cinema.

4. **The students have discussed the pollution problems since last week.**
- The pollution problems have been discussed by the students since last week.

5. **Have the thieves stolen the most valuable painting in the museum?**
- Has the most valuable painting in the museum been stolen by the thieves?