一般汽车雾灯控制中开雾灯必须先开（）。
参考答案：灯光开关
根据句意，用括号内所给词的适当形式填空。
1. I think everyone has two________(foot).
2. The old man has a serious________(ill).
3. Mr Chen is often________(stress) out.
4. It's easy to stay________(health).
5. My brother's________(speak) Chinese is very good.
说出布氏硬度値350HBW10/3000/30中各符号的含义。
