You are given the following returns on "the market" and stock F during the last three years. We could calculate beta using data for years 1 and 2 and then, after year 3, calculate a new beta for years 2 and 3. How different are those two betas, i.e., what's the value of beta 2 - beta 1?
a) Cannot be determined
b) Positive
c) Negative
d) Zero