Because of the Russian gas limit to Europe, attempts _______ to use botanical fuel as a source of power.

A．have made

B．having made

C．are being made

D．will be making

我国写字楼按功能可以分为（）三种类型。

A.一级、二级、三级

B.甲级、乙级、丙级

C.大型、中型、小型

D.单纯型、综合型、商住型