What did Jack remind me to do before going to bed?

The correct choice is "Lock the door," and it aligns well with common safety practices before going to bed. When someone reminds you to lock the door, it implies a concern for security and a desire to ensure that the home is safe while occupants are sleeping. This is a typical reminder that one might receive from a friend or family member, highlighting the importance of taking precautions.

The other options may not reflect the usual priorities before bedtime. For instance, forgetting the door would suggest carelessness, leaving the light on could represent either a choice of comfort or wastefulness, and opening the window might imply a need for fresh air but could also introduce safety issues depending on the situation. Therefore, locking the door stands out as a responsible and practical suggestion in this context.