保证他们可用英语怎么说

你可以用"guarantee"来表示"保证"的意思。这个词来自拉丁文"garantia"，意思是"保证，保障"。

例句：

I can guarantee that the product will be delivered on time. (我保证产品会准时交付。)
The seller guarantees the authenticity of the item. (卖家保证物品的真实性。)
The company guarantees a full refund if you are not satisfied with the product. (如果你对产品不满意，公司保证全额退款。)