Write at least 60 words about the topic“The Fun of Learning ________(playing the piano / doing housework / playing football / English /…) ”. (以“学……的乐趣”为题写一篇不少于60个词的短文，标点符号不占格。)

Use the following points as a reference. (以下问题仅供参考)

1. your experience of learning…… (give an example)

2. reason (s) you think it is fun learning……

假设消费者两个时期内分别有I₁和I₂的收入，市场利率为r(假定储蓄与借款的利率相同)，试用替代效应和收入效应解释利率的改变与储蓄的关系。