assure  v.    保證

例:

I can assure you of their loyalty to the company.

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reassure   v.   使安心

例:

The doctor reassured Vincent that his mother would be fine.

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insure     v.   為......投保

例:

It is wise to insure yourself against chronic disease.

chronic   adj. 慢性的

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ensure     v.     確保

例:

Hard work ensures your success.

例:

Please ensure that all lights are turned off before you leave.

例:

Your cooperation will ensure Malcolm Industries' continued success.