Answer:
There were no trains that went to the Pacific Coast.
Explanation:
The given sentence implies that there were no trains that went to the Pacific Coast at the time the Pony Express was developed. Trains would be with no doubt a faster and more convenient way to deliver mail than men riding horses. If there were trains going to the Pacific Coast at the time, there would be no need for the Pony Express.
The war isn't mentioned at all, which is why we can automatically eliminate the second and fourth options as correct.
The third option is incorrect because we can't conclude that previous forms of transit to the West did not include mail. They probably did, because the mail had to be delivered somehow, but they weren't fast at delivering.
This is why the first option is the correct one.
