When my girlfriend rings me out of the blue, I'm in a good mood for the rest of the day.
我突然接到女朋友的电话,接下来的一整天我的心情都很好。
This is because they had no natural enemies until the arrival of humans and therefore did not need to develop flying wings.
这是因为人类到达这里之前,这些鸟没有天敌,因此,它们不需要发育飞行的翅膀。