【正确答案】 D

【答案解析】Use TACTIC 4, Chapter 12. Could x and y be equal? Yes; the two small triangles could be right triangles, and x and y could each be 40. Must they be equal? No; see the figure at the right, in which x ＜ y. Neither column is always greater, and the columns are not always equal (D).
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【正确答案】 D

【答案解析】If a and b had to be integers, the greatest a + b could be is 49 (when the numbers are 1 and 48). However, the variables do not have to be integers. If a =. 1, and b = 480, then ab = 48, and a + b = 480.1. Neither column is always greater, and the two columns are not always equal (D).