___itcarefullycanwehopetofindawaytosolvethechallengingp...

问题详情：

___ it carefully can we hope to find a way to solve the challenging problem.

A．When we observe                                       B．When to observe                         

C．That we should only observe                   D．Only by observing

【回答】

D

知识点：倒装与省略

题型：选择题