The accurate summary of the United States’ involvement and military role in World War I is:
The U.S. became involved in World War I after the Zimmermann Telegram and sent troops to provide military reinforcements and support.
The Zimmermann Telegram, which was a secret diplomatic communication from Germany to Mexico proposing a military alliance, played a significant role in swaying public opinion in the United States against Germany, leading to U.S. entry into the war. The Selective Service Act was a means to draft soldiers but was not the primary reason for entering the war. The other options listed are not accurate.