1.answer意思是“回答”，是一个普通用词，使用范围广，可以做及物动词和不及物动词。它只对问题或者请求答复，包括以口头书面及动作来回答，也可以用于指对别人的指责或者控告的答复。比如：
I cannot answer you right now.我不能马上达答复你。He answered the examination paper quite well.他试卷答的相当好。
Please answer my question.请回答我的问题。He refused to answer the charges against him.他拒绝对他的指控进行答辩。
2.reply当“回答，答复”讲时，常用于比较正式的场合或者做出比较正式的答复，含有针对别人的观点，经过周密思考后的答复的意思。比如：
I sent in my application, and the university replied immediately.我递交了申请书，该大学马上给我答复。He replied that he had caught cold and would not come to the reception.他答复说，他感冒了，所以不能来参加招待会。
I asked him several questions, but he did not reply although it seemed tom me that he had been thinking about them seriously.我问他几个问题，他都没回答，虽然我感到他似乎认真地考虑了这些问题。
3.需要注意的是：answer后面跟的宾语是telephone、door、bell时，表示的是对这些事物“做出反应”，是一种固定搭配，即answer the telephone（接电话）、answer the door（开门）、answer the bell（应门）。这里就不能用reply。比如：
She answered her phone on the first ring.她在响第一声铃时就接了电话。
reply to 和answer有时后面接相同的宾语，从字面上看，它们的意思相同，但实际含义不太一样。比如：
Did he answer your letter?他回复你的信了吗？
I will reply to his letter at once.我马上给他回信。
例1中的answer your letter主要侧重写回信，说明已收到来信，回信的内容并不一定重要。而 reply to his letter则侧重回信的内容，对来信中提到的每一个点都要逐一做出答复，有较强的针对性。再比如：
answer his salute； reply to his salute
answer his salute表示对于他的敬礼做出反应，比如点头、招手、微笑都可以。而 reply to his salute表示以礼相还，也就是说他对你敬礼，你也对他敬个礼
