题目

一Could you please ______ the music? My baby is sleeping． 一Sorry．I will do it right away． A．open up               B．turn down            C．drop by                  D．dress up 答案：B科学家最新研制了一款微型无人侦察机——“蜂鸟”.为了减轻其质量，该侦察机的材料应具有的特点是    A．硬度高B．熔点低C．密度小D．导热性好