She sleeps nine hours.为什么nine前不要加for?

She sleeps nine hours.为什么nine前不要加for? sleeps for nine hours 的同义句 sleeps for nine hours同义句 He sleeps for nine hours over night的问句 She usually sleeps (nine hours) a day对括号内提问 （）（）does she usu Danid usually sleeps for nine hours every night 改为同义句? Dacid usually sleeps for nine hours every day 同义句在等 David usually sleeps for nine hours every night.改为同义句怎么改?急 kate sleeps nine hours every night中对nine hours提问 He sleeps nine hours every day.[对nine hours划线提问] sleep nine hours和sleep for nine hours My little brother sleeps nine hours every day.(划线提问)