The correct response is:
Fearing an American invasion in China, Mao Zedong dispatched troops to support North Korea’s armies.
General MacArthur's successful landing at Inchon and the subsequent advance of U.S. forces towards the Chinese border alarmed China, leading Mao Zedong to intervene by sending Chinese troops to assist North Korea. This significant intervention altered the course of the Korean War and ultimately led to a stalemate.