当O₂、SO₂、SO₃的质量比为2∶4∶5时，它们的物质的量之比为[ ]

A．2∶4∶5  

B．1∶2∶3

C．1∶1∶1  

D．2∶2∶3

—Is this your bike?

—No, it isn't _____. It's _____. [ ]

A. my; her

B. mine; hers

C. my; your

D. mine; their