30. There are three lamps, A, B, and C. The red switch controls A and B, the blue switch controls B and C, and the green switch controls A and C. Initially, all three lamps are on. After Peter Pan presses the red switch once, A and B both turn off. Then Peter Pan presses another 19 switches, and in the end, only one lamp is on. If Peter Pan pressed the red switch a total of 8 times, which lamp is on?
$\mathrm{C}$