10. In the cube $A B C D-A_{1} B_{1} C_{1} D_{1}$, $E$ is the trisection point of $A_{1} A$, and $F$ is the trisection point of $C_{1} C$, with $A E=$ $2 A_{1} E, C F=2 C_{1} F$. A section is made through $B$, $E$, and $F$ in the cube. Among the following projection diagrams of the section on the corresponding faces, which one is incorrect? ( ).
10. When projected onto the $D_{1} D B B_{1}$ face, it should form a line segment, so the answer is D.