题目

. --- The company spent thousands of dollars to promote its new product. --- They _____: the world itself was more than ready to buy. A. shouldn’t have bothered                 B. needn't have bothered C. couldn’t have bothered                  D. mustn’t have bothered 答案：B先化简，再求值：÷（a-），其中a、b满足式子|a-2|+（b-）2=0．