世界最大的黄土堆积区是( )。

单项选择题Sole proprietorships are predominantly started. It has following characteristics A、they are easily and cheaply setup. B、the proprietorship life is limited to the business owner's life. C、all business taxes are paid as individual tax. D、All of the choices.

单项选择题实施保教任务的基本单位( )。A.幼儿园B.年级组C.班级D.小组