Which of the following statements is correct?

a. If corporate tax rates increase, then all corportate WACCs will also increase.

b. If market interest rates increase, then all corporate WACCs will decrease

c. If a company's overall exposure to systematic risk increases, then the company's WACC will decrease

d. If corporate tax rates increase, then corporate WACCs will decrease

e. If a company's unsystematic increases, then the WACC will increase.