【正确答案】 D

【答案解析】Use TACTIC 4, Chapter 12. Could y = 20? Yes, if the large triangle were equilateral, x would be 30 and y would be 20. Must y = 20? No, if x = 45, y = 10. (Note: Since the figure may not be drawn to scale, the triangle could be any triangle with a 60° angle.) Neither col-umn is always larger, and the columns are not always equal (D).

【正确答案】 B

【答案解析】You don't have to solve for a and b. If a -b > a + b, then b is negative and Column B is greater.
**You could solve. Adding the two equations yields
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