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

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。