电话的听筒部分需要定期清洁。

The ___mouthpiece of the telephone needs regular cleaning.

这位记者成为了抗议者的代言人，在电视上传达他们的诉求。

The journalist served as a ___mouthpiece for the protesters, voicing their demands on TV.

打橄榄球时，他总是戴着护齿套以防受伤。

He always wears a ___mouthpiece when playing rugby to prevent injuries.