So, I was on my cell phone with Leah, who used to date Justin, who I saw in the library studying the anatomy of a certain friend of ours.

当时，我正用手机跟曾和贾斯汀约会的利亚通话的时候，我看见他(贾斯汀)在图书馆和我们的一个朋友在学习解剖学。

youdao

We are always sure that our friend will understand why we acted in a certain way.

我们总是确信朋友会理解为什么我们那样做。

youdao

There is a certain nonsense tale which a friend used to tell with such effect that her hearers became helpless with laughter, but which for some reason never seemed funny to me.

有这么一个故事：是一个朋友常常给她的听众讲的一个故事，每次她讲的时候听的人都忍不住要大笑。可是，也许是由于某种原因吧，我觉得这个故事压根儿就不好笑。

youdao

The friend suggests a certain insect repellent.

你朋友建议使用一种驱虫剂。

I've already 课堂 - SpeakingMax英语口语达人

You use the "let's" pattern when you suggest to a friend, a colleague or to anybody that you do something a certain way.

当你在向朋友、同事或任何其他人提出建议，希望大家以某种方式做某事的时候，你可以使用“let's”句型。

Let's 课堂 - SpeakingMax英语口语达人

So, let us say that I had signed an agreement with a friend, that he pay me a googolplex of dollars under certain conditions, would that make the situation exponentially worse?

FORBES: Shocking Truth: Newsworthiness Bias Crushes Women and Children

Some skulking around the future App Store layout from 9to5 Mac reader Sonny Dickson has shown an as yet unreleased Twitter 4.3 release carrying "more interactive experiences" for links within certain posts -- in other words, expect a multimedia extravaganza if a friend really digs that New York Times article.

ENGADGET: Twitter for iOS 4.3 gets early teases from Twitter itself and the App Store, promises gobs of in-tweet content