写出矩形具有而一般平行四边形不一定具有的一条性质( ).
对角线相等(答案不唯一)
—What time will Mr. Brown be back to China?
—Sorry. I don’t know______.
A.when did he go abroad
B.why he is going abroad
C.how soon will he be back
D.how long he will stay abroad
离子选择性电极对测量阴离子时,其电位正比于(a是离子活度)()。
A.-lnaR内
B.aR
C.-lnaR
D.lnaR