句型转换，每空一词。 

1. His ruler is in the box. (对画线部分提问)

    ___    ____ his ruler?

2. This room is Lucy and Lily's. (改为选择疑问句)

    _ _     this room Lucy's ____ Lily's?

3. Is he your friend? (改为复数)

    ___    ____ your ____?

4. These are our apples. (改为单数)

    ___    is ____ ____. 

5. The boy is all right today. (对画线部分提问)

    ___    ____ the boy today?

6. They can see a bird in the tree. (对画线部分提问)

    ___    ____ ____ see in the tree?

传递函数是对加到方块上的输入信号的特定运算符号，运算结果即是输出信号。输出信号的因次应等于输入信号的因次和方块中传递函数因次的（）。

A、之和

B、之差

C、之积

D、之商