At present, most of the motorcycle engines use the traditional naturalaircooling systems which have simple structures but unideal cooling effect.
目前，大多数摩托车发动机均采用传统的自然风冷却系统。
2
These homes were all built to take advantage of simple, naturalcooling methods–no air conditioner required.
这些住宅都利用简单、自然的冷却方法而建——无需空调。
3
But naturalcooling techniques have been used for as long as humans have been building homes; after all, the modern air conditioner is a relatively recent invention.