水准尺可以分为单面水准尺和双面水准尺两种。双面水准尺分为黑红两面。黑面尺底端从零开始，红面尺底端从一常数开始，该常数一般为（）。

--- You are drinking too much.

--- Only at home. No one _______ me but you.

A．is seeing

B．had seen

C．sees

D．saw