I wish I could,but I have to meet my friend.
我倒想去，但我得去接一个朋友。

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1. Thank you very much, but I've already had a date with Mr.Green.非常感谢，不过我已经约了格林先生。

2. Oh,what a pity! I'm going to a lecture.哦，真可惜！我马上要去听一个讲座。

3. I'm afraid I can't. But thank you all the same.我恐怕不能去。不过我还是要谢谢你。

4.I'd rather not.But thank you very much for inviting me.我还是不去了。但还是要谢谢你邀请我。