一般台式机的前面板上与声音相关的接口数为（）
A.1个
B.2个
C.3个
D.4个
参考答案：B
A large number of students in our school ______ from the countryside, the number ____ growing these years. [ ]
A. is, has been
B. are; has been
C. is, have been
D. are, have been
下列有关乙酸的表示正确的是（ ）
A．球棍模型：
B．电子式：
C．分子式：CH20
D．结构式：
