Answer
a) The four planes that form the faces are ABC, ACD, ABD and BCD.
b) $\overset\longleftrightarrow{AD}$, $\overset\longleftrightarrow{BD}$, $\overset\longleftrightarrow{CD}$
Work Step by Step
a) Each side of the tetrahedron is a plane.
b) You can see in the figure that 3 lines lead to point D.
