Read the following passage carefully, and answer the questions given below them, in the context of the passage.
Strange, un-fathomable happiness of thinking of seeking knowledge for its own sake. So much of our life is spent in solving problems to avoid immediate pain or to bring immediate profit, so much of our training is aimed at bringing practical or pragmatic effect designing and running machines, buying, selling, cooking, furnishing. investing, spending, so many worthy results are obtained by purposeful planning and directed thinking that we forget how true and inexhaustible is the happiness of pure knowing. Everyone has tasted it. It is born in children. It goes to school with them, and is too often killed there by tired or practical teachers. But in some, it survives and unlike other delights it endures for life. To spend $50$ or $60$ years in studying the structure of fishes or the relation between logic and language, the history of the Incas or the rules of comets, the geometry of Non-Euclidean space, the literature of leei and/or the anatomy of the brain, to acquire, systematic and record new knowledge or any subject without expectation of benefit making except by extending its range of understanding that is to pass a happy and valuable life, usually tempered at the close by regret that another $50$ years could not be added, in which to learn more and still more. It is the purest and least selfish satisfaction known to man, except those of creating a work of art and healing the sick. It is, Aristotle said, to share the activity of God-himself, his eternal life of pure contemplation
"Everyone has tasted it" is mentioned in the paragraph. 'It' here refers to :
- Directed thinking
- Happiness of pure knowing
- Pure knowing