在面向对象方法中，允许作用于某个对象上的操作称为 【3】 。
参考答案：方法
18．_________a US visitor visa twice, the old couple finally gave up their hope of going to America to experience Thanksgiving Day.
A．Having been refused
B．Being refused
C．Having refused
D．To be refused
技术供水系统的水温、水压和水质不满足要求时，会有什么后果？
