Answer:
Option: d) the transcontinental telegraph was completed.
Step-by-step explanation:
The Pony Express started in America as a to mail delivery service that covered the areas of between Missouri and California. The mails were delivered by the riders who would ride hundreds of miles with switching to fresh horses in each station on his way. The Pony Express went out of business after the opening of the transcontinental telegraph because telegraph could be sent faster with less cost.