Difficult in practice, this new technique hasn’t been applied.
A. operated
B. to be operated
C. operating
D. to operate
网友回答
A. operated
B. to be operated
C. operating
(答案→)D. to operate
解析：此处相当于because it is difficult to operate in practice，省略because it is之后就变成了 difficult to operate in practice. 句意：因为这种新技术很难在实践中操作，所以它没有被应用。