In order to get good marks in the coming exam, my son ______late every night in the past three weeks.

A．studies

B．studied

C．has been studying

D．was studying

常温下，将0.1 mol·L^-1 NaOH溶液与0.04 mol·L^-1硫酸溶液等体积混合，所得溶液的pH等于

A．2.0

B．4.0

C．10.0

D．12.0