大黄的乙醇提取浓缩液,经乙醚萃取得到乙醚萃取液,再用5%NaHCO3水溶液萃取得到的是()
A.大黄素
B.大黄酸
C.大黄酚
D.芦荟大黄素
E.大黄素甲醚
参考答案:B
Although the working mother is very busy, she still ____ a lot of time ____ children.
A.devotes…on
B.devotes….to
C.spends…to
D.spends…in
什么是变压器分级绝缘?