$\begin{array}{1 1} A. a \to 3, b \to 4, c \to 1, d \to 2 \\ B. a \to 4, b \to 3, c \to 1, d \to 2 \\ C. a \to 4, b \to 3, c \to 2, d \to 1 \\ D. a \to 2, b \to 3, c \to 1, d \to 4 \end{array} $