Which one of the following is the best definition of the term beta as it applies to the concept of risk and return?

1. The guaranteed return on a short-term treasury security which will be earned in the future.

2. The difference between the expected return on a risky asset and the expected market return.

3. The alpha possible from a risky investment

4. The systematic risk of an investment within a diversified portfolio.

5. All of the above are correct definitions.