$\begin{array}{1 1}(A)\quad they\;must\;be\;mutually\;exclusive\\(B)\quad the\;sum\;of\;their\;probabilities\;must\;be\;equal\;to\\(C)\quad(A) \;and\;(B)\;both\;are\;correct\\(D)\quad None\;of\;the\;above\;is\;correct\end{array}$
