本文主要讨论作为形容词时的用法。
1. alternate [ˈɔːltərnət , ˈɔːltərneɪt]
n.候补;代替者;代理人
v.(使)交替;(使)轮流
adj.交替的;轮流的;间隔的;每隔(…天等)的
John has to work on alternate Sundays.
约翰每隔一周就有一个星期日得上班。
She works on alternate days.
她隔天工作。
Lesley had agreed to Jim going skiing in alternate years.
莱斯莉已同意吉姆每隔一年去滑一次雪。
He felt alternately hot and cold.
他感到忽冷忽热。（副词）
alternate laughter and tears时笑时哭
Her mood alternated between happiness and despair.
她一会儿高兴一会儿绝望。(动词)
Alternate cubes of meat and slices of red pepper.
交替放置肉丁和红辣椒片。
We had a week of alternate rain and sunshine.
天忽晴忽雨，已有一个星期。
这个词做动词也是经常的一个四六级或考研水平的常见考点：
Professor Smith and Professor Brown will alternate in giving the class lectures.
史密斯教授和布朗教授将轮流上课。(六级真题)
2. alternative [ɔːlˈtɜːrnətɪv]
adj.可供替代的;另类的;非传统的;其他的，两种或多种可供选择的；
n.可供选择的事物
Do you have an alternative solution?
你有没有别的解决办法？
alternative comedy/lifestyles/values
非传统喜剧 / 生活方式 / 价值观
alternative health care.
传统的医疗保健
alternative energy (= electricity or power that is produced using the energy from the sun, wind, water, etc.)
替代能源（指太阳能、风能、水能等）
You can be paid in cash weekly or by cheque monthly: those are the two alternatives.
你的工资可以按周以现金支取，或按月以支票支取。二者可选其一。
There were alternative methods of travel available.
还有其他可选的旅行方式。
Alternative medicine has been gaining credence recently.
近来替代疗法越来越得到大众的认可。
If you like alternative comedy you'll love this book.
如果你喜欢另类喜剧的话，你就会喜欢这本书。
They had a right to seek alternative employment.
他们有权另谋高就。
He wants to make sure that schools are committed to providing alternative education.
他想确保学校尽力提供新型教育。
In retrospect, I wish that I had thought about alternative courses of action
回想起来，我真希望自己当时考虑过其他做法。
In Belgium only qualified doctors may practise alternative medicine
在比利时只有资质合格的医生才能从事非传统医学工作。
There are alternative answers to your question.
你的问题有几个可供选择的答案。
Alternative sources of protein must be found when meat and fish are not available.
在没有肉和鱼的情况下，必须找到其他蛋白质来源。
此时alternative=others,其他的
protein [ˈproʊtiːn] n.蛋白质
There is no alternative: the President must approve the bill if Congress passes it.
别无选择：如果国会通过该法案，总统必须批准。
此时alternative=other choice;名词
It is advisable to have an alternative plan.
最好有一个替代方案。(有一个替代方案是明智的。)
此时alternative=substitute
When travelling , you are advised to take travellers’ cheeks ,which provide a secure alternative to carrying your money in cash.
旅行时建议你携带旅行支票，这为携带现金提供了一种安全的变通办法。
when引导的是句子的时间状语。which引导的是travelers' checks为先行词的非限定性定语从句。
which引导非限制性定语从句的结构通常都是逗号+which。which既可以指主句的整个句子，也可以指主句中的名词，或主句中的其他从句。
此处to为介词，其后跟的是现在分词短语carrying...，其中介词短语in cash为方式状语。
此时alternative是名词，可供选择的事物
provide……to提供……给
