一级相变
参考答案：相变时两相的化学势相等，但化学势的一阶偏微商不相等。发生一级相变时有相变潜热和体积的变化。
John was about to go back to sleep ______ suddenly his bedroom became as bright as day．
A．after
B．when
C．while
D．until
每个Java小应用程序必须定义为( )。
A．Applet类或JApplet类的子类
B．JFrame类的子类
C．Frame的子类
D．Window的子类
