The pony express went out of business when
a) at& t completed the national telephone network.
b) the radio was invented.
c) the mexican war ended in 1846.
d) the transcontinental telegraph was completed.
e) the civil war began in 1861.

Option: d) the transcontinental telegraph was completed.

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.

the authority to tax.