要配制pH为7的缓冲溶液100ml,需要量取0.5 mol·L-1 Na2HPO4和0.5mol·L-1 KH2PO4溶液各大约是多少体积?
A. 共轭碱 39ml
B. 共轭碱 31ml
C. 共轭酸 61ml
D. 共轭酸 69ml
在“职工”表中有姓名、性别和生日等3个字段,要查询所有年龄大于50岁职工的姓名、性别和年龄,正确的SQL命令是
A. SELECT姓名,性别,YEAR(DATE())-YEAR([生日])AS年龄FROM职工WHEREYEAR(Date())-YEAR([生日])>50
B. SELECT姓名,性别,YEAR(DATE())-YEAR([生日])年龄FROM职工WHEREYEAR(Date())-YEAR([生日])>50
C. SELECT姓名,性别,YEAR(DATE())-YEAR([生日DAS年龄FROM职工WHERE年龄>50
D. SELECT姓名,性别,YEAR(DATE())-YEAR([生日])年龄FROM职工WHERE年龄>50