题目

 We have been told that the contract is          for one year starting from the fifteenth of June of this year. A. effective         B. complicated        C. practical           D. significant 答案：A12．已知甲数为2a，乙数比甲数的2倍多3，丙数比甲数的2倍少3，求甲、乙、丙三数的积．当a=-2.5时，积是多少？