Answer:
The correct answer is letter "D": Roll.
Explanation:
American economist Richard Roll (born in 1939) criticized the diversification of assets portfolio stating that there could never be such a thing since it would require to consider every investment in every market included all types of existing securities. Rolls was doubtful about the usefulness of the Capital Asset Pricing Model (CAPM) which is based on portfolio diversification.
Besides, according to Roll, the Beta coefficient -a measure of stock's volatility- was only useful while grouping various securities but not when analyzing them alone.
