保证怎么说用英语

To guarantee something means to promise or assure that something will happen or be true. Here are a few ways you could say this in English:
"I guarantee that it will be done on time."
"We guarantee the quality of our products."
"I can guarantee your satisfaction with our services."
"We guarantee that our prices are the lowest you'll find."
Note that when you guarantee something, you are taking responsibility for making sure that it happens or is true. In some cases, this may also involve providing compensation if the guarantee is not fulfilled.