题目如下：

Assume that the instantaneous utility function u(C) in equation(2.1) is ln(C).Consider the problem of a household maximazing(2.1) subject to (2.6).Find an expression for C at each time as a function of initial wealth plus the present value of labor income, the path of r(t), and the parameters of the utility function.

我看的是英文版的，所以大家凑合看吧，呵呵，我对答案有点不解，答案中，第二个等式，一般来讲是不等式，此题为什么可以取等式？第六个等式下面As long as ......(which it must be),the integal is ......如果不成立此题就无法解？

还望大家不吝赐教，谢谢！多谢了！

PS：公式2.1和2.6我在此处没法写，答案里面显示的有。