Final answer:
Nick Watson, a former U.S. Army Ranger, established a nonprofit that uses mountain climbing to assist veterans with the transition to civilian life.
Step-by-step explanation:
Nick Watson, a former U.S. Army Ranger, started a nonprofit to help veterans readjust to civilian life, which utilizes mountain climbing as a means of rehabilitation. This can be combined into one sentence with a relative clause as follows:
“Nick Watson, a former U.S. Army Ranger who started a nonprofit to help veterans readjust to civilian life, uses mountain climbing for their rehabilitation.”
By combining the two sentences with the relative clause ("who is a former U.S. Army Ranger"), it creates a single sentence that gives both pieces of information—Nick Watson's background and his initiative of starting a nonprofit to aid veterans through mountain climbing.