Which of the Following Statements Is False

Which of the following statements is false?

A) The portfolio that contains all shares of all stocks and securities in the market is called the efficient portfolio.
B) The market portfolio is an efficient portfolio.
C) We can measure the systematic risk of a security's return by its beta.
D) Because it is difficult to find data for the returns of many bonds and small stocks, it is common practice to use the S&P 500 portfolio as a proxy for the market portfolio, under the assumption that the S&P 500 is large enough to be essentially fully diversified.