—Is this your bike?

—No, it isn't _____. It's _____. [ ]

A. my; her

B. mine; hers

C. my; your

D. mine; their

下列说法错误的是( )。

A．口腔内经常存有大量细菌

B．刷牙、喝水时可清除部分口腔细菌

C．口腔清洁可以减少口臭和各种口腔疾病

D．老年人一般都吃得比较少，可以不必每天刷牙、漱口