I’m pretty certain it’s d because it does not state anywhere that the sound waves are not powerful enough to make the vocal engine useful. hope this helps brainlist would be much appreciated :)
Answer:
我不完全了解原因,因为我是初学者,但似乎还可以
Wǒ bù wánquán liǎojiě yuányīn, yīnwèi wǒ shì chū xuézhě, dàn sìhū hái kěyǐ
对不起,浪费我的时间,我不明白
Duìbùqǐ, làngfèi wǒ de shíjiān, wǒ bù míngbái
i basically said sorry and you can translate the rest
“We count sheep to sleep, don’t you?”