(2013·江西，19)Marco Polo is said to have sailed on ________ Pacific Ocean on his way to Java in ________ thirteenth century.

A．the；a

B．a；/

C．/； the

D．the；the

流体的流动阻力与（）有关.

A.湿周长度

B.水力半径

C.管路的长度

D.A、B、C都正确