[单选题]
An electric circuit wvs(lr 5r+v2n l;gcyqz ,2nr 33b(l ktdith em hi; 3d jkk6uj15xf4velt9g 0cf $ϵ$ and internal resistance r is connected to a variable resistor R which varies from 0 Ω to 6Ω.
The variation of the power dissipated in the resistor R with the value of the resistance R is shown in the graph.
What is the value of $ϵ$, if the maximum dissipated power is when R is equal to the internal resistance of the battery $r$ ?