As a teacher,  I seldom give my students so difficult a problem ________ they can not work out.

A．that

B．if

C．in order that

D．as

我国第一个国家正式批准的BOT模式建设的项目是( )。

A．广西来宾电厂

B．沙角B电厂

C．岭澳二期

D．大亚湾核电站二期