1、The most difficult part of the game must be ___（sleep）.

1、The most difficult part of the game must be ___（sleep）.
为什么答案是sleeping?不用被动语态么?
2、关于电话用语.可不可以说 who is this而不是who‘s that?
不好意思。第一题打错了。
是
1、The most difficult part of the game must be ___（sweep）。