Fixed income analysis部分一个关于convexity的问题

Fixed income analysis教材Reading 66后面练习题第8题不太明白，答案中说A high coupon bond will exhibit negative convexity. A  low coupon bond will exhibit positive convexity. 为什么呢？

麻烦老师或明白的同学帮助解答一下，谢谢啦！