蔬菜和水果是人体获得______的主要食物原料。
A.维生素
B.糖类
C.脂肪
D.蛋白质
参考答案:A
Only by learning more about different cultures _______ avoid misunderstanding during international cooperation.
A.we can
B.we should
C.should we
D.can we
简述空隙大小的影响因素。