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# The room temperature is $+ 20^{\circ}C$ when outside temperature is $- 20^{\circ}C$. Room temperature is $+ 10^{\circ}C$ when outside temperature is $- 40^{\circ}C$. The temperature of the radiator heating the room is

$\begin {array} {1 1} (1)\;70^{\circ}C & \quad (2)\;60^{\circ}C \\ (3)\;50^{\circ}C & \quad (4)\;40^{\circ}C \end {array}$

(2)$60^{\circ}C$