在20℃时，物质所具有的密度称为（）。
A、标准密度
B、实际密度
C、视密度
D、相对密度
参考答案：A
Jack would like to go to the cinema with dad, but the film is ______ for adults only.
A．admitted
B．promised
C．intended
D．permitted
Most of us see a doctor ______ when we get a cold or something.This won't cost us a lot.
A．suddenly
B．immediately
C．occasionally
D．frequently
