----are changed into electrical signals.

----are changed into electrical signals.

该当选b the sound waves

这边sound 是定语waves暴涨,化装wave,就像apple tree,而不是apple's tree 或 apples' tree.

币小哥资源讯息:以man, woman做定语的短语,如man/woman doctor 在变复数时变为 men/women doctors,既变前一局部,也变后一局部

这下领会了吧

sound wave 声波

这边是复数sound waveswaves暴涨,以是是b