Rewrite the following sentences as required. (根据所给要求，改写下列句子，每空格限填一词)
（1）、Lily had a good time during her stay in Beijing. (改为否定句) Lily a good time during her stay in Beijing.
（2）、We have a class meeting once a week. (对划线部分提问) do you have a class meeting?
（3）、Many countries make laws to stop smoking in public. (改为被动语态) Laws by many countries to stop smoking in public.
（4）、The river pollution is serious in our country today. (改为感叹句) the river pollution is in our country today!
（5）、Robert is so short that he can't yet reach the pears on the table. (改为简单句) Robert isn't to reach the pears on the table.
（6）、I can't give you better advice than that. (保持原句意思) I can give you advice.
（7）、Bill didn't go to bed until he finished writing the letter at 11:45 last night. (保持原句意思) Bill until he finished writing the letter at 11:45 last night.
