$\begin {array} {1 1} (A)\; \alpha_1 + \alpha_2 & \quad (B)\;\large\frac{(\alpha_1+ \alpha_2)}{2} \\ (C)\;\large\frac{(\alpha_1 \alpha_2)}{(\alpha_1+ \alpha_2)} & \quad (D)\;\large\frac{2(\alpha_1 \alpha_2)}{(\alpha_1+ \alpha_2)} \end {array}$
