Final answer:
The speed limit at a railroad crossing is set for safety purposes and varies by jurisdiction; thus, the correct speed limit should be obtained from local traffic laws or signage at the crossing.
Step-by-step explanation:
The speed limit at a railroad crossing where you cannot see for 400 feet down the tracks in both directions tends to be lower for safety reasons, as you need adequate time to perceive and react to an oncoming train. However, the speed limit can vary by jurisdiction, and the specific answer should be obtained from local traffic laws or signage at the crossing. For the purpose of this exercise and without a specific jurisdiction provided, none of the answers listed can be confirmed as correct. Therefore, always check the local traffic laws or railroad crossing signage for the accurate speed limit.