In a problem with a train and two observers, one (A) standing next to the rail while the other one (B) sittingat the rear endof the train. The train is moving seen by Awhile it is stationary seen by B. Event 1: B turns on a flash light in his hand aiming at a mirror hanging at the front end of the train; Event 2: the light illuminated on the mirror and reflected; Event 3: the reflected light reached B. Which time intervals of a pairs of events measured by an observer is considered as proper time and why? (The answer can be more than 1 or just 1 or even none of them.) (a) Event 1 and Event 2 observed by A; (b) Event 1 and Event 3 observed by A; (c) Event 2 and Event 3 observed by A; (d) Event 1 and Event 2observed by B; (e) Event 1 and Event 3 observed by B; (f) Event 2 and Event 3 observed by B

In a problem with a train and two observers, one (A) standing next to the rail while the other one (B) sittingat the rear endof the train. The train is moving seen by Awhile it is stationary seen by B. Event 1: B turns on a flash light in his hand aiming at a mirror hanging at the front end of the train; Event 2: the light illuminated on the mirror and reflected; Event 3: the reflected light reached B. Which time intervals of a pairs of events measured by an observer is considered as proper time and why? (The answer can be more than 1 or just 1 or even none of them.) (a) Event 1 and Event 2 observed by A; (b) Event 1 and Event 3 observed by A; (c) Event 2 and Event 3 observed by A; (d) Event 1 and Event 2observed by B; (e) Event 1 and Event 3 observed by B; (f) Event 2 and Event 3 observed by B