1: not good because do not know the weights of the other 5 books
2: among the ten books, 5 books weigh 1.2 pounds.
condition 1: all 5 books are the heaviest books, not right, because 6<6.6 condition 2: some of the 5 books are the heaviest books, some are not, still not right, it is same as saying 1.2 can be the heaviest and non-heaviest at the same time, not right condition 3: all 5 books are not in the heaviest books, right, but we do not know how the heaviest 5 books weigh so 2 alone is not good