把people place litter baskets under the trees改为被动式

Litter baskets have been placed under the trees,but people s Litter-baskets have been placed under the trees汉语意思 litter baskets have been placed under the trees 这句话是被动语态 求变成 litter baskets have been placed under the trees为什么不用has we have placed litter-baskets under the threes改成被动句 Someone asks you if the litter baskets have been emptied yet these pairs of tramers are under the trees 改为单数句 All the people must stop (){litter} 把You mustn't drop litter in the schoolyard改为同义句怎么改? People must down the trees place under the care of sb .They often sleep under trees.改为否定句