Almost all of the books published in the past 150 years were printed on acidic paper. Unfortunately, every kind of acidic paper gradually destroys itself due to its very acidity. This process of deterioration can be slowed if the books are stored in a cool, dry environment. Techniques, which are now being developed, to deacidify books will probably be applied only to books with historical significance. If all of the statements in the passage above are true, which one of the following must also be true? ['If a book was published in the past 150 years and is historically insignificant, it will probably deteriorate completely.', 'Almost all of the books published in the past 150 years will gradually destroy themselves.', 'Books published on acidic paper in 1900 should now all be at about the same state of deterioration.', 'If a book is of historical significance and was printed before 150 years ago, it will be deacidified.']