A: Firstly, allow me to introduce myself. My name is John Brown, manager of the company. B: ______

A．You must be mistaken. I don't know you at all.

B．Hello, Brown, I haven't seen you for ages.

C．Very nice to see you, Mr. Brown.

D．Hi, John! Welcome to our company.

一只船沿河顺水而行的航速为30千米/小时，已知按同样的航速在该河上顺水航行3小时和逆水航行5小时的航程相等，则此船在该河上顺水漂流半小时的航程为( )

A．1千米

B．2千米

C．3千米

D．4千米