Consider Two Blinking Warning Lights $3000 \mathrm{~m}$ Apart Along a Railroad Track

Consider two blinking warning lights $3000 \mathrm{~m}$ apart along a railroad track. These lights flash simultaneously in the ground frame. Let $W$ be the event of the west light blinking, and let $E$ be the event of the east light blinking. $A$ train moves eastward along the track at a relativistic speed $\beta$ . Suppose an observer in the train passes the west light just as event $W$ happens. By carefully measuring when the light from event $E$ arrives and calculating the distance between the two lights (by observing how long it takes to travel between the lights at the known speed $\beta$ ) , the observer is able to infer when event $E$ actually happened in the train frame. The observer concludes that

A) Event $W$ happened before event $E$ in the train frame.
B) Events $W$ and $E$ were simultaneous in the train frame.
C) Event $E$ happened before event $W$ in the train frame.
D) One cannot determine unambiguously which event occurs first in the train frame.