Final answer:
Jack Swigert was going to retire after the Apollo 13 Mission.
Step-by-step explanation:
The correct answer is Option 4: Jack Swigert. Jack Swigert was not originally scheduled to be part of the Apollo 13 mission, but he replaced Ken Mattingly after Mattingly was exposed to measles. The Apollo 13 mission was the seventh crewed mission in NASA's Apollo space program and was intended to be the third mission to land on the Moon. However, an oxygen tank explosion caused the mission to be aborted and the crew had to return to Earth safely.