Which of the following statements is CORRECT?

a. Beta is measured by the slope of the security market line.

b. If the risk-free rate rises, then the market risk premium must also rise.

c. If a company's beta is halved, then its required return will also be halved.

d. If a company's beta doubles, then its required return will also double.

e. The slope of the security market line is equal to the market risk premium,