ufo前面是加a.
例如：You know, I saw a UFO last night. 你知道，我昨天看见UFO了。
He thought they were UFO, not a military training.
我认为它们是UFO，而不是一次军事训练。
He reported seeing a UFO himself several years ago.
他报告几年前自己亲眼看到一不明飞行物。
They are making a study of UFO.
他们正在对不明飞行物进行研究。
温馨提示：
