alternate与alternative的差别?
1 `alternate'
Alternate （交替的）动作、事件或过程在彼此之后定期发生。
.．the alternate contraction and relaxation of muscles
交替收缩肌肉的交替收缩和松弛
电学中的交流电就是alternate current
如果某件事发生在（alternate days,） 隔天，它发生在某一天，然后第二天不发生，然后在它之后的一天再次发生，以此类推。事情也可以在每隔几周（alternate weeks）、几个月或几年发生。
We saw each other on alternate Sunday nights.
The two courses are available in alternate years.
2 `alternative'
你可以用alternative来描述可以用的，可以拥有的东西，而不是其他的东西。
Motorway closed. Please use an alternative route.
高速公路关闭。请使用另一条路线。
There is, however, an alternative approach.
然而，还有另一种方法。
注意，在美式英语中，alternate表示这个意思。
Every effort is being made to offer customers alternate travel arrangements.
Alternative也可以作名词。An alternative to something指的是你可以拥有或做的其他事情。
Many food suppliers now provide non-dairy alternatives to cheese and milk.
Community service is often used as an alternative to prison.
There is no alternative to hard work.
你也可以说某人有两个或更多的选择（two or more alternatives），意思是他们有两个或更多的行动路线可以选择。
I had two alternatives: give up or carry on.
