$B_1$, $B_2$ and $B_3$ are three identical lamps. They are joined to a battery with zero internal resistance, as shown. At first the switch is closed. The switch is then opened and lamp $B_3$ goes out. What change occurs to the brightness of lamps $B_1$ and $B_2$ when the switch is opened?
- Abrightness of lamp $B_1$ decreases, brightness of lamp $B_2$ decreases
- Bbrightness of lamp $B_1$ decreases, brightness of lamp $B_2$ increases
- Cbrightness of lamp $B_1$ increases, brightness of lamp $B_2$ decreases
- Dbrightness of lamp $B_1$ increases, brightness of lamp $B_2$ increases