The price of aluminum was sharply reduced when people discovered a new refining process with the aid of（）

A．Aluminum is widely used in transportation.
B．Aluminum is also used in many parts of airplanes.
C．Aluminum is being used extensively in the building industry.
D．Aluminum is not used in its pure form.

A．lightweight, rustproof but not easily shaped into different forms
B．heavyweight, rustproof and easily shaped into different forms
C．lightweight, rustproof and easily shaped into different forms
D．lightweight and easily shaped into different forms but it is easy to become rusty