《物权法》关于业主的权利与义务关系的说法，正确的是( )。

A．可以放弃权利不履行义务

B．不得以放弃权利不履行义务

C．可以通过合同约定其享有权利而不履行义务

D．可以不放弃权利也可以不履行义务

根据所给的汉语提示，转换下列句型。

1. Stamps are used for sending letters.(对画线部分提问)

     _____ are stamps used_____?

2. The little boy was made to do heavy work by the boss.(改为主动语态)

    The boss _____ the little boy _____ heavy work.

3. They asked me to come the next day.(改为被动语态)

    I_____    ___ to come the next day.

4. The factory was built in 1956.(对画线部分提问)

        __  was the factory_____?

5. So far, we haven't had any trouble.(改为同义句)

    We _____had any trouble _____ now.