The numbers 1, 2, 3 and 4 are written separately on four slips of paper. The slips are then put in a box and mixed thoroughly. A person draws two slips from the box, one after the other, without replacement. Describe the following events: A = The number on the first slip is larger than the one on the second slip. B = The number on the second slip is greater than 2. C = The sum of the numbers on the two slips is 6 or 7. D = The number on the second slips is twice that on the first slip. Which pair(s) of events is (are) mutually exclusive?