Intertemporal substitution in labor supply describes changes in labor supply in response to changes in (跨期——中文由在线翻译而来，仅供参考)
选项：

A: personal tax rates.个人税率。
B: investment spending.投资支出。
C: the real interest rate.实际利率。
D: consumer demand for goods.消费者对商品的需求。