You are standing on a train platform watching a high-speed train pass by. A light inside one of the train cars is turned on and then a little later it is turned off.

(a) Who can measure the proper time interval for the duration of the light: you or a passenger on the train?

(b) Who can measure the proper length of the train car: you or a passenger on the train?

(c) Who can measure the proper length of a sign attached to a post on the train platform: you or a passenger on the train?

In each case explain your answer.