I.词语辨析：
1. below / under
below: 指（高度、职位、数量、年龄）在……之下”，（能力等）低于……
e.g. 100 metres below sea level, ten degrees below zero
below还可作后置定语，“下面的、以下的”
e.g. the figures below：下面的数字
under: 指“在垂直的下方”或“级别、数量、标准等低于……
e.g. Let’s sit under the tree. There are many children under 12 years of age.
2. know: 知道，明白
e.g. He knows exactly what he’s doing.
know of: 知道有，听说过……
e.g. I have never know of such a thing before.
