Train and Tunnel - Solution

1. D
2. A
3. C
4. D
5. In the tunnel frame points A and D are simultaneous so the train fits inside the tunnel exactly.
   But in the train frame D is simultaneous with C and A is simultaneous with B. So when the nose of the train emerges from the tunnel at D, the tail is still at C, and when the tail finally enters the tunnel at A, the nose is already at B, so the train is much longer than the tunnel in the train frame.
   As we can see from the space-time diagram, this is not a contradiction, just two different ways of seeing the same reality. (Please review the section on Lorentz Contraction.)