单项选择题无阻尼单自由度振动系统的质量块的振动位移函数为，则质量块的振动速度函数为（ ）。 A、 B、 C、 D、
单项选择题Which of the following is not very polite? A、Would you mind spelling your name again for me? B、Could you spell your name, please? C、Spell your name. D、Please spell your name.
