The first political passengers on modern railroad cars were a president, a senator,and a governor that had been traveling to Washington,DC.together on the Liberty Express in 1907.
A
B The first political passengers on modern railroad cars were a president, a senator, and a governor, who traveled
E A president, a senator, and a governor were the first political passengers on modern railroad cars traveling.
a an E both have some errors as follows:
a) verb tense is wrong; that modifies someone
e) what "travelling" is disigned to nmodify? if it is used to modify cars, the meaning is definitely distorted. if it is to modify those guys, a "," should be added.(作为伴随状语)