问题
选择题
Difficult _____ in practice, this new technique hasn’t been applied.
A．operated
B．to be operated
C．operating
D．to operate
答案
答案：D
题目分析：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。