If exactly one of the trains arrives after the Wooster but before the York, then which one of the following could be ...

When Mehran goes over the question on the video, the stem asks, "What must be true?" on the practice question it asks, "what could be true?" these two are very different. Both A and E COULD BE TRUE but only A MUST BE TRUE. Whoever is posting these needs to change the question stem. It seems to be a Typo and I was confused as to why I got it wrong until I checked the video example and noticed the startling difference in the stem on this question. Please change it.