WACC

Which of the following is the CORRECTLY describes the effect on the weighted average cost of capital (WACC) if tax rates decrease?

A The WACC will increase because the cost of debt will increase
B The WACC will decrease because the cost of debt will decrease
C The WACC will decrease because the cost of equity will decrease
D The WACC will increase because the cost of equity will increase

My answer is A but the Scheme is C without any explanation

i had done imaginary calculation as in lets say its an 8% loan notes and the old tax rates is 30% and the new one is 15%

30%
year
1 (100)
2 5.6
3 5.6
4 5.6
5 105.6
IRR = Kd = 6%

15%
1 (100)
2 6.8
3 6.8
4 6.8
5 106.8
IRR = Kd = 7%

isnt the cost of debt increases as the tax rate drop? or am I wrong somewhere in my imaginary calculation