This topic examines the knowledge of materialist dialectics. "Although the world is safe, it will be dangerous if you forget to fight" means that if the world is safe, it will be dangerous if (a country) forgets to prepare for war. It embodies the sense of hardship of "being prepared for danger in times of peace". From the perspective of Marxist philosophy, the contradiction between "safety" and "danger" can be transformed into each other under certain conditions. Item a is correct. Item B: Everything starts from reality, which embodies the philosophical truth that "practical viewpoint is the primary viewpoint of dialectical materialism epistemology, and practice is the basis of cognition". Item b is wrong. Item C: External cause is the condition for the change and development of things, and the philosophical truth embodied is "the dialectical relationship theory between internal cause and external cause in the law of unity of opposites." Item c is wrong. Item D: We should adhere to the viewpoint of seeking truth from facts, which embodies the philosophical truth that "practice is the basis of cognition and practice plays a decisive role in cognition". Item d error.