单项选择题 硬聚氯乙烯塑料原料来源丰富，下列四种材料中，哪个不是硬聚氯乙烯塑料原料的来源？（）

单项选择题 产品费用中，有一部分费用与产量的多少无关，称为( )。

未知题型 48题A.People spend more time at shopping centers that have trees.B.In hot countries, urban forests are cool places for walking and other healthy exercises.C.But you are not in rural area.D.Trees take pollution out of the airE.In 2033, it will have 5 million trees.F.It has many kinds of birds in the country