鞘翅
参考答案：
翅的质地为角质，坚硬，翅面无可见翅脉的翅叫鞘翅。
--- Thanks for your dinner .
--- _______________. [ ]
A. You eat well .
B. You are welcome.
C. Sorry , it isn't good .
D. Let's go home .
两列相干的平面简谐波振幅都是4cm，两波源相距30cm，相位差为π，在两波源连线的中垂线上任意一点P，两列波叠加后合振幅为：
A．8cm B．16cm C．30cm D．0
