64 A. For the dihedral angle $M-A B-N$, construct a plane $P \perp A B$, and then construct a plane $Q / / A B$ and perpendicular to plane $N$. At this point, regardless of the size of the dihedral angle $M-A B-N$, plane $P$ and $Q$ form a right dihedral angle, so Proposition A is not true.
Through the midpoint $E$ of side $C D$ of the equilateral triangle $B C D$, construct a perpendicular line to the plane $B C D$, and take point $A$ on this perpendicular line such that $A E=E C$, then all the lateral faces are isosceles triangles. However, $A-B C D$ is not a regular tetrahedron. Therefore, Proposition B is not true.
For Proposition C, when the vertex angle of the axial section is greater than $90^{\circ}$, the area of the axial section is not the largest. Therefore, Proposition C is also not true.
Proposition A: "If the two half-planes of one dihedral angle are perpendicular to the two half-planes of another dihedral angle, then these two dihedral angles are equal or supplementary."
Proposition B: "A triangular pyramid with a base that is an equilateral triangle and lateral faces that are isosceles triangles is a regular triangular pyramid."
Proposition C: "The section through two generatrix of a cone has the maximum area when it is the axial section."
The number of true propositions is
A. 0
B. 1
C. 2
D. 3