the opening ceremony is a great occasion.it is essential _______for that.
A for us to be prepared B that we are prepared.
..可是我觉得应该是 for us to prepare
答案说如果是B的话 应该原句是 it is essential that we should prepare for that opening ceremony （那如果按照是A的逻辑 是被动的话 这里不应该就是...should be prepare）
为什么不是 for us to prepare
it is essential ___（for us to be prepare）____for that.
这里的it 指us的话。为什么要用被动。