用一张硬卡片先后快拨和慢拨木梳的齿，听到卡片声音发生变化．这个实验用来探究______．

用硬纸片把一个喇叭糊起来，做成一个“舞台”．台上小人在音乐声中翩翩起舞，这个现象说明______．

We don’t care about how Obama won the Nobel Peace Prize but _______matters for us is ______he will make his effort to bring a peaceful world to us. （原创）

A．that; how

B．which; whether

C．it; that

D．what ; whether