— Excuse me, sir. Is the swimming pool open all day as it used to be? 

— _____. only from 6:00p.m to 10:00p.m.[ ]

A．That's right

B．Yes, of course

C．Sorry, I'm not sure

D．Sorry, I'm afraid not

重载的关系运算符和逻辑运算符的返回类型应当是______。