If $e_1,e_2,e_3,e_4$ are the four elementary outcomes in a sample space and $P(e_1) = .1, P(e_2) = .5, P (e_3) = .1$, then the probability of $e_4$ is ______.

Question

$\begin{array}{1 1}(A)\;0.3\\(B)\;0.4\\(C)\;0.5\\(D)\;0.13\end{array}$