塑料壁纸的种类（）.
A、普通墙纸
B、发泡墙纸
C、特种壁纸
D、以上都对
参考答案：A, B, C, D
In our life, we can work hard on one task , and then another. In this way, all your dreams can be realized.
A．at a time
B．on time
C．at the time
D．all the time
三极管构成放大器时，根据公共端的不同，可有（）种连接方式。
A.1
B.2
C.3
D.4
