在探究杠杆平衡条件得实验中，我们曾多次改变力和力臂的大小，这样做的目的主要是为了（   ）

    Do you like watching TheVoiceofChina? If you like it, you may know Zhang Lei.He ____(win) first place in TheVoiceofChinaIV.He comes from Heilongjiang.He was good at singing when he was young.He likes playing the g____He can sing many songs.People feel very ____(relax) when they hear Zhang Lei's songs.He wants to be a ____(sing) like Lao Lang in the f____ Do you like his songs?