用所给单词的正确形式填空。

1. Last football match was very ______ (excite).

2. ______ (stay) up late is bad for your health.

3. Why don't you ______ (give) up smoking?

4. My parents didn't feel ______ (good) last Sunday.

5. ______ (not walk) on the lawn. We must protect (保护) our environment.

A公司与B公司签订了购买5辆汽车的合同。就在B公司将汽车交付A公司时，被工商行政管理部门查出该批汽车是走私物品而予以查封。根据我国《合同法》关于合同效力的规定，该买卖汽车合同属于( )。

A．有效合同

B．无效合同

C．效力待定的合同

D．可撤销的合同