句型转换。

1. Is the book under the sofa? (做否定回答)

    ______, ______.

2. The keys are on the dresser. (对画线部分提问) 

    ______ ______ the keys?

3. Is it in the backpack? (改为复数形式)

   ______ ______ in the backpack?

4. I know the teacher. (改为否定句)

    I ______ know the teacher.

5. They are on the sofa. (改为一般疑问句) 

    ______ ______on the sofa?

合成尖晶石代替天然尖晶石时被称为仿制宝石，而代替橄榄石，海蓝宝石等时则被称为合成宝石.