问题如下：
Tax loss harvesting is most effective when:
选项：
A. there are few similar investment opportunities for the security with the loss.
B. the taxpayer is currently in a relatively high tax environment.
C. the taxpayer is currently in a relatively low tax environment.
解释：
B is correct.
Tax loss harvesting is best used when tax rates are relatively high.
老师请问，为何不选C？是不是future tax rate is lower才能对投资者有利？