(2 points) Suppose that a group of 150 students have joined at least one of the chat rooms: one on auto racing, one on bicycling, and one for college students. For simplicity, we call these rooms A. B, and C respectively. In addition. 90 students joined room A; 50 students joined room B: 70 students joined room C: 15 students joined rooms A and C; 12 students joined rooms B and C: 10 students joined all three rooms. How many students joined both chat rooms A and B? O 140 students 27 students O 43 students O Cannot be determined