药物的离解常数用下列哪种符号表示（）。
A.pH
B.pK
C.pHa
D.pKa
E.以上都不是
参考答案：D
Mike didn't ________ his parents and friends _ , he won the first in the competion. [ ]
A. let; down
B. make; happy
C. keep; clean
D. make; down
平面上有三个点，可以确定直线的条数是 ( )
A．1条
B．2条
C．3条
D．1条或3条
