This suggests a relationship between military power and food production, which can be associated with themes of national strength and self-sufficiency. Therefore, the correct option is (B) communism and nationalism.
Given the options you've provided:
(A) communism and capitalism - This seems less likely, as the image does not clearly contrast two different economic systems.
(B) communism and nationalism - This option appears more plausible as communist propaganda often emphasizes the strength and unity of the nation, and the image could be interpreted as showcasing the protection and provision afforded by the state.
(C) war and the environment - While there are soldiers and agricultural elements present, there is no clear indication of an environmental theme.
(D) industry and agriculture - This could also be a valid interpretation, as the train could symbolize industry, and the cargo could represent agriculture, showing the link between these two sectors in a national economy.
Given the typical themes of Chinese propaganda, particularly during the era when such imagery was common (mid-20th century), the most likely relationship being depicted here is between communism and nationalism (B), as it promotes the idea of a strong, self-sufficient communist state that can defend itself and feed its people.