要约可以撤回和撤销。撤回或撤销要约的通知应当在要约到达受要约人之前或者与要约同时到达受要约人。()
参考答案:对
Can I have some rice, please? [ ]
A. Sure. Here you are.
B. Thank you.
C. Everything' s ready.
常用的调节阀的执行机构有哪几种?