在面向对象方法中，一个对象请求另一对象为其服务的方式是通过发送( )。
A．调用语句
B．命令
C．口令
D．消息
参考答案：D
—That actor often joins in different activities in Beijing. Do you know ________?
—For 5 years. [ ]
A. how soon he will come back
B. how long he has stayed there
C. when he went there
D. when he will come here
球罐的预热温度应根据以下条件确定：焊接材料、气象条件、接头的拘束度和（）。
A．焊件长度
B．焊件厚度
C．焊件韧性
D．焊件塑性
