Scientists are trying to develop a special material they will make use of in space.A. th

问题补充：

Scientists are trying to develop a special material, they will make use of in space.

A. that

B. what

C. it

D. one

答案：

A. that

B. what

C. it

(答案→)D. one

解析：句意，科学家们正在尝试发明一种特殊的物质，一个可以在太空中使用的物质。one 指代 a special material, 其他的that和it 是特指的，不能代替 a special material, what不能引导定语从句，所以这道题只能选one。