I don’t think portals carry the momentum with them. It’s as if the train is a moving tunnel. So A.

I love this comment section. Perfect balance of people actually trying to discuss and people getting pissy because their answer can be the only right one.

I don't know shit but when I try and picture it happening in my head I can only see A being correct, think Doctor Strange portals. When he moves a portal the person comes out stationary

C. A train flies out of the blue portal

If it's A, then it figures to me that the blue portal would enact some force on the structure on which it's placed when the tied up people plop out

This comment section reminds me a bit of these cringe powerscalers, discussing Saitama vs Son Goku in the comments of a YouTube video.

B, but only their bellies; the portal is above most of their bodies, and their heads and ankles will get cut off for being off even the track.

A if the trolley is going slow

B if the trolley is going fast.

Someone take this a step further and make the train an airplane on a treadmill