Complete the sentence with the best relative pronoun.
Guion S. Bluford was a pilot in the U.S. Air Force ____later became an astronaut and, in 1983, was the first African American to travel in space aboard the space shuttle Challenger.
Guion S. Bluford was a pilot in the U.S. Air Force ____later became an astronaut and, in 1983, was the first African American to travel in space aboard the space shuttle Challenger.