goodidea后面为什么加s

表示复数，例如：

1.The book is a cornucopia of good ideas.这部书里有无数好主意。

2.Amy: Me too. I'm just thinking about the gift. Have you got any good ideas?艾米：我也是。但我还在想礼物。你有什么好主意吗?

3.He has good ideas but he isn't practised in the art of marketing.他有好的构想，但推销技巧却嫌生嫩。