题目

Reportedly yesterday a group of American soldiers were walking along the road in Iraq when a bomb was _____, three of whom were killed.          A. set about              B. set off           C. set up           D. set out 答案：B多种乐器合奏比单一乐器演奏的声音更丰富，因为不同种类的乐器各自具有独特的（ ）A．音调B．响度C．音色D．频率