―What do you think of this dress, darling?

―Er...sorry, dear. I       _______. What did you say?

A．didn't listen

B．hadn't listened

C．haven't listened

D．wasn't listening

校正pNa表时，采用pNa4标准溶液标定，此溶液中Na＋离子浓度为（）mg/L。

A、23；

B、2.3；

C、0.23；

D、0.023。