"Other volunteers took the lead role in making sure that gifts for certain communities stay together and get the process going and making sure that the individuals and volunteers who were there to wrap had a supply of wrapping papers and scissors and tape and everything.

VOA: standard.2009.12.24

There's a certain pragmatic element behind this, basically we want to make sure that every human being has a dignified life.

这后面是有实用的因素，因为我们想确保,每个人都过上有尊严的生活。

普林斯顿公开课 - 人性课程节选

to make sure that you speak with someone who is very knowledgeable about the prices of certain things.

一定要跟某些很了解价格行情的人谈谈。

关于购买艺术品 - SpeakingMax英语口语达人

Then again, if you are not certain of something you can say "I'm not sure."

同样的，如果你对于一件事没有把握，你可以说“I'm not sure.”

I'm sure 课堂 - SpeakingMax英语口语达人

You can say "I'm sure that" to express the idea that you are certain of something.

你可以用 "I'm sure that" 来表达你对某件事有把握。

I'm sure 课堂 - SpeakingMax英语口语达人