1. 向…保证；使…确信；使…放心
    If you assure someone that something is true or will happen, you tell them that it is definitely true or will definitely happen, often in order to make them less worried.

assure在线翻译

    e.g. He hastened to assure me that there was nothing traumatic to report...
           他忙不迭地向我保证，并没有什么悲惨的事要诉说。
    e.g. 'Are you sure the raft is safe?' she asked anxiously. 'Couldn't be safer,' Max assured her confidently...
           “你确定木筏安全吗？”她不安地问道。“再安全不过了，”马克斯信心十足地向她保证道。

2. 保证，确保（得到）
    To assure someone of something means to make certain that they will get it.

    e.g. Last night's resounding victory over Birmingham City has virtually assured them of promotion...
           昨晚大胜伯明翰城队实际上已确保他们能够晋级。
    e.g. Ways must be found to assure our children a decent start in life.
           必须想办法保证我们的孩子有一个不错的人生开端。

3. 我可以向你保证；相信我
    You use phrases such as I can assure you or let me assure you to emphasize the truth of what you are saying.

    e.g. I can assure you that the animals are well cared for...
           我可以向你保证动物们得到了精心照顾。
    e.g. This may sound trivial, but I assure you it is quite important!...
           这听上去也许微不足道，但是，相信我，它十分重要！