下面哪种沟通不属于非语言沟通（）。
A、面露微笑
B、咳嗽
C、眉头紧蹙
D、打电话
参考答案：D
If you feel tired and sick of fat food, that is _______ you have to go to the hospital for a medical examination.
A．why
B．when
C．whether
D．what
润滑剂的主要作用是什么？简述其具体内容？
