adj.未通知的，未预告的，未打招呼的

The President made an unannounced visit to the hospital to see the wounded soldiers.
总统未事先宣布就到医院探望受伤的士兵。
There was an unannounced power cut, leaving the entire building in darkness.
未经预告的停电使整栋大楼陷入黑暗。
The company's CEO conducted an unannounced inspection of the factory.
公司的首席执行官对工厂进行了未宣布的检查。
She was startled by an unannounced guest at her doorstep.
她被一位不速之客在门口出现吓了一跳。
An unannounced fire drill was held to test the staff's response time.
进行了一次未事先通知的消防演习，以测试员工的反应时间。
The celebrity made an unannounced appearance at the charity event, surprising everyone.
这位名人未事先通知就出现在慈善活动中，令所有人惊讶。
The teacher gave us an unannounced quiz on Friday afternoon.
老师在周五下午突然给我们做了一个小测验。
The mayor made an unannounced visit to the school to observe the teaching methods.
市长未事先通知就到学校参观教学方法。
An unannounced guest at dinner can cause some inconvenience for the host.
晚餐时未邀请的客人可能会给主人带来一些不便。
The police conducted an unannounced raid on the suspected drug den.
警方对涉嫌的毒品窝点进行了未事先通知的突击搜查。