 The key is that if the car is behind door 2 the host must open door 3, but if the car is behind door 1 the host can open either door.Another way to understand the solution is to consider the two original unchosen doors together (Adams 1990; Devlin 2003, 2005; Williams 2004; Stibel et al., 2008).As Cecil Adams puts it (Adams 1990), "Monty is saying in effect