ANSWER is OPTION 3 i.e. imagination.The passage speaks of the humanistic and imaginative elements that contribute to education.As per the third sentence of the passage, that reads, "And it is only through imagination that men become AWARE of what the world might be..." The correct option is 3.The other OPTIONS are not entirely wrong, however, they are elements born from imagination. As mentioned in the second sentence, literature, paining, ARCHITECTURE, etc. are essential to the life of imagination. Therefore, without imagination we wouldn't know what the world might be and it would just remain mechanical or trivial.