4. If each face of a tetrahedron is not an isosceles triangle, then the minimum number of edges with unequal lengths is
A. 3
B. 4
C. 5
D. 6
Answer:
A tetrahedron with equal opposite edges is called an isosceles tetrahedron, which means the minimum number of edges with unequal lengths is 3. Therefore, the answer is $A$.