Option 1: Compassionate -> This means showing sympathy and concern for others, which is similar to altruistic, not opposite.
Option 2: Constant -> This means unchanging or continuous, which is unrelated to the meaning of altruistic.
Option 3: Selfish -> This means concerned primarily with one's own interests and pleasure, which is the direct opposite of altruistic (selfless concern for others).
Option 4: Intelligent -> This means having good mental capacity or understanding, which is unrelated to altruistic behavior.
Hence, Option 3: Selfish -> Altruistic means showing selfless concern for others' well-being, while selfish means being concerned only with one's own interests, making them perfect antonyms -> correct