Being a teacher always encouraging students to think for themselves, I won't tell them answers until they __________ on a math problem for more than an hour.

A．have worked

B．will have worked

C．will have been working

D．had worked

“和平统一、一国两制”的科学构想，是从解决 问题开始提出来的。

A．台湾

B．香港

C．澳门

D．.香港和澳门