已知△ABC的一个内角为120°，并且三边长构成公差为4的等差数列，则△ABC的面积为（ ）。
面向对象的模型中，最基本的概念是对象和【 】。
In plugging submerged holes on a vessel，rags，wedges，and other materials should be used in conjunction with plugs to（）.
A.reduce the water pressure on the hull
B.reduce the water leaking around the plugs
C.prevent progressive flooding
D.reduce the possibility of stress fractures
