Question

Difficult _____ in practice, this new technique hasn’t been applied

1. A.
   operated
2. B.
   to be operated
3. C.
   operating
4. D.
   to operate

Answer 1

D
试题分析：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。
考点：考查非谓语动词的用法。