Đáp án tham khảo, có thể sai: 1a, 2d, 3b, 4b, 5bc, 6ad, 7d, 8ab, 9d, 10d, 11c, 12d, 13ad, 14b, 15d, 16cd, 17d, 18c, 19b, 20bd, 21b, 22bc, 23b, 24d, 25ab, 26d, 27a, 28ac, 29c, 30c, 31b, 32bc, 33b, 34c, 35c, 36a, 37ac, 38d, 39bd, 40ac, 41c, 42d, 43a, 44d, 45d, 46a, 47c, 48c, 49d, 50ac, 51ad, 52ab...