用所给词的适当形式填空.(1).There are-------(student)on the piayground.(2).How many---------------(ruler)are there in the pencil-box?(3).There------------(be)some posters and a photo on the wall.(4).Are there---------------(some)pens on your desk?(5).There are nine----------(hundred)books on the shelf(书架).（6）.There are two-----------------(library)and fifteen--------------(class)my school.(7).We all-----------(child).(8).Kate and Mary are----------------(friend).