问题
选择题
Have you realized the difficulty we have ____ the problem?
A．worked out
B．to work out
C．work out
D．working out
答案
答案：D
考查固定句型。have difficulty/trouble (in) doing sth.“做某事有困难”。句意“你意识到我们在解决这个问题时，遇到的困难吗？”根据固定句型可知，选D。