____可分为可回收垃圾、不可回收垃圾、有毒有害垃圾等几类。
水平桌面上放一本书,书的质量为0.3kg,则书的重力____ N;若书与桌面的接触面积为0.05m2,则书对桌面的压强是 ____ Pa.
Most Americans don't like to get advice from members of their family.