Final answer:
The lap portion of a seatbelt should be positioned snugly across the abdomen, over the upper thighs, to distribute force over the pelvis in an accident, preventing serious internal injuries.
Step-by-step explanation:
The lap portion of the seatbelt should be positioned across the abdomen to maximize protection against injuries. When properly positioned, the lap belt should be snug across the upper thighs, not the stomach. This ensures that in the event of an accident, the force is distributed over the stronger parts of your pelvis and not on the soft tissue of your abdomen, which could result in serious internal injuries.