问题
选择题
The city was difficult ________, _________ was defended by an army of 6,000 men.
A．to be taken; which
B．to take; that
C．to take; which
D．to be taken; that
答案
答案：C
The city was difficult to take =" It" was difficult to take the city. 只要这两种句型能够互换，不定式就得用主动的形式。