It took a long time for the effective use of natural gas .
A. making
B. being made
C. to make
D. to be made
网友回答
A. making
B. being made
C. to make
(答案→)D. to be made
解析：句意，能够有效地使用天然气，将花费很长的时间。分析句子结构，这里需要不定式作定语，“natural gas”与“to make”之间是被动关系，所以应该使用不定式的一般式的被动形式。