Which of the following possible portfolios is least likely to lie on the efficient frontier?（ ）
| Portfolio | Expected Rehurn | Standard Deriation |
| W | 7% | 5% |
| X | 9% | 12% |
| Y | 11% | 10% |
| Z | 13% | 15% |
Portfolio X has a lower expected return and a higher standard deviation than portfolio Y. X must be inefficient.