胶体物质有何特点?
胶体主要存在地表水中特别是随着季节的变化水中含有大量的悬浮物,如粘土淤泥等胶体均匀布于水体中它对膜的危害性极大。
A campus emergency ______ occur at any time of the day or night, weekend, or holiday, with little or no warning.
免费的网站请分享给朋友吧