i know how to calculate the portfolios, ( expected return / standard deviation), but how am i supposed to know if theyre on the efficient fontier????

6. Which of the following possible portfolios cannot lie on the efficient frontier? Portfolio Expected Return Standard Deviation 1 10% 6% 2 12% 6% 3 14% 12% 4 14% 10% A. Portfolios 1 and 4 B. Portfolios 2 and 3. Portfolios 1 and 3. D. Portfolios 2 and 4. C