certify: usually applies to a written statement, especially one carrying a signature or seal: ~ied that the candidate had met all the requirements.   书面证明候选人符合要求


attest: applies to oral or written testimony usually from experts or witnesses and often under oath or by word of honor: ~ed the authenticity of the document.    word of honor诺言保证=pledge，介词用by


witness: applies to the subscribing of one's own name as evidence of the genuineness of a document: two persons who ~ed the signing of the will.   （subscribe有2个意思 1、订阅to pay money regularly for something，如which journals does the library subscribe to图书馆订阅了哪些报刊？如he subscribes regularly to Amnesty International他定期向大赦国际捐款(或会员续费)，如the tour of Edinburgh is fully subscribed去爱丁堡旅游的名额已经满了 2、支持support，如I've never subscribed to the view that either sex is superior to the other我从不同意(支持)性别有优劣之分的观点。  这里subscribe的用法很罕见，应该是表示签名to write down one's name，字典里找不到这样的用法）


vouch: suggests that the one who testifies is a competent authority or a reliable person who will stand behind an affirmation: willing to ~ for the woman's integrity.

certify(书面)证明: 通常指书面声明，附签名印章，attest证明: 指专家证人的口头或书面证明，需宣誓承诺，witness签名作证: 表示用自己签名作为证据，证明文档真实，vouch担保: 表示作证的人可靠权威，愿意提供担保


记忆方法: 1）首字母CAWV洞穴<==作证

         2）作证的意思是证明某事为真meant to testify to the truth or genuineness of something.  （这一组的基础词是testify作证证明，常表示在法庭上作证证明to give a statement of truth, especially in court，介词用to，如the film testifies to the courage of ordinary people during the war这部电影证明了老百姓在战争期间的英勇，如there are several witnesses who will testify for the defence有几名证人愿意为被告作证，如she refused to testify against her husband她拒绝出庭作证指控丈夫。名词testimony)