将铁架台、漏斗、烧杯、玻璃棒几种仪器组装后,可进行的净化水的操作是
A:过滤
B:沉淀
C:吸附
D:蒸馏
一根6.28米长的绳子,恰好围一棵大树绕了2圈,这颗大树的横截面积是多少?
There was not library in my old school. ____
已知数列an满足an+1=an+1n∈N*,且a2+a4+a6=18则log3a5+a7+a9等于( )