请根据要求改写下列句子，每空一词。
Her father has been on the phone since half an hour ago. （对划线部分提问）
_________ _________ has her father been on the phone?
I think diving is the most difficult activity of all. （保持句意基本不变）
I think diving is more difficult than __________ __________ activity.
We can put those machines on the ground floor of the building. （改为被动语态）
Those machines can __________ __________on the ground floor of the building.
The beach is a nice place for tourists.  （改为感叹句）
___________ __________ nice place for tourists the beach is!
Pingping is so energetic that he can be a good monitor. （改为简单句）
Pingping is ___________ ___________ to be a good monitor.