12. Given that the four vertices of tetrahedron $P - A B C$ lie on the surface of sphere $O$, with $P A = P B = P C$, $\triangle A B C$ is an equilateral triangle with side length 2, $E , F$ are the midpoints of $P A , A B$ respectively, and $\angle C E F = 90 ^ { \circ }$, then the volume of sphere $O$ is A. $8 \sqrt { 6 } \pi$ B. $4 \sqrt { 6 } \pi$ C. $2 \sqrt { 6 } \pi$ D. $\sqrt { 6 } \pi$ II. Fill-in-the-Blank Questions: This section has 4 questions, each worth 5 points, for a total of 20 points.
D
12. Given that the four vertices of tetrahedron $P - A B C$ lie on the surface of sphere $O$, with $P A = P B = P C$, $\triangle A B C$ is an equilateral triangle with side length 2, $E , F$ are the midpoints of $P A , A B$ respectively, and $\angle C E F = 90 ^ { \circ }$, then the volume of sphere $O$ is\\
A. $8 \sqrt { 6 } \pi$\\
B. $4 \sqrt { 6 } \pi$\\
C. $2 \sqrt { 6 } \pi$\\
D. $\sqrt { 6 } \pi$
II. Fill-in-the-Blank Questions: This section has 4 questions, each worth 5 points, for a total of 20 points.\\