Preserve is to maintain something in its original status, which means to prevent something from changing.
Preserve是维护保持已有或原始状态的意思。目的是避免改变。名词是保护区的意思。
Example:
The forest land is very old, and it was preserved as a natural perservation zone.
那片森林非常古老，被设定为了自然保护区。
Reserve is to retain for future use.
Reserve是预留、预占，以便未来使用的意思。
Example:
I let the restaurant reserve a table for us this Friday night.
我让餐厅给我们预留了一个周五晚上的桌位。
Conserve is to do your best to maintain or protect something (usually the natural environment) from harm or danger.
Conserve是指人类有序的开发、改变已有事物但尽所能保持或者保护事物(通常指自然环境)免受伤害或危险。
Example:
We should do our best to help conserve endangered forest and animals.
我们应该尽最大所能去帮助保护处于危险的森林和动物。
