86．She cleans her room twice a week．(对划线部分提问)

________ ________ ________ she her room?(对划线部分提问)

85．The twins are shorter than Tim．(同义句)

Tim ________ ________ than the twins．

84．My brother did his homework yesterday．(改为否定句)

My brother ________ ________ his homework yesterday．

83．Don’t forget ________ (close) the windows when you leave．

82．Ann spends about half an hour ________ (exercise)every Sunday afternoon．

81．They ________ (not visit) the Great Wall next week．

80．Thank you for ________ (invite) us．

79．I’m sorry．I can’t．I have to ________ (help) my mom．

78．Doing eye exercises ________ (be)good for you．

77．You are never too young 　________ (start)doing things．