The Decay $\pi ^ { - } \rightarrow \mu ^ { - } + \bar { v } _ { \mu } + \bar { \nu } _ { e }$

Multiple Choice

The decay $\pi ^ { - } \rightarrow \mu ^ { - } + \bar { v } _ { \mu } + \bar { \nu } _ { e }$ is not possible because

A) L_e is not conserved.
B) L _$\mu$ is not conserved.
C) quark number is not conserved.
D) all of the above are not conserved.
E) only L_e and L _$\mu$ are not conserved.