Which combination best explains the worldwide expansion of socialist movements?

Correct answer: Successful revolution Comintern foreign training and communist parties

Socialist movements expanded internationally through a combination of political example, organisation, and practical support. The success of the Russian Revolution demonstrated that a revolutionary movement could seize state power. The Comintern helped maintain international connections, spread political guidance, and encourage the creation of communist parties in different countries. Foreign training and exchanges further supported activists.

Together, these factors carried socialist ideas beyond Russia and helped movements develop common language, organisation, and strategy while responding to local conditions. The other combinations refer to institutions or activities that did not promote the worldwide growth of socialist movements. Hence option B is correct. It contains all the major elements named in the historical explanation.