You must be disappointed at losing the chance.

失去这次机会，你肯定很失望吧。

I told them that they would be disappointed at the news.

我告诉他们，听到这个消息，他们会失望的。

You must be disappointed at the first sight of me, I guess.

所以我相信同学们看到我的第一眼一定感到非常的失望。

However, I suspect many will be disappointed at quite how keenly he talked down the importance of electoral reform in some parts of the interview.

但是，很多人也会对他在采访中极力强调选举的重要性，想要说服大家感到很失望。

I am writing to tell you that we were quite disappointed with your service. We had booked a table, but when we went there at the time as arranged, only to be told there were no seats available.

我想写信告诉你，我们对你的服务非常失望。 我们已经预订了一张桌子，但是当我们按预定的时间去那里的时候，却被告知没有座位了。