propellants：

A variable pitch propeller is made _____ a boss with separate blades mounted into it.

PROPELLER技术又称为（)

When the propeller blades are integral with the hub, the propeller is called a _____.A.bui

Fuel oil transfer systems used onboard diesel propelled vessels are required to have _____

Propeller running at ____ are generally efficient.A.high speedsB.medium speedC.low speedsD

Barges which carrier most of the heavy freight on rivers and canals are usually propelled