mumble|mumbled|mumbling

他咕哝着说这是在浪费时间。

He ___mumbled something about it being a waste of time.

别咕哝了，请大声点说！

Stop ___mumbling and speak up, please!

她太紧张了，演讲时开始含糊不清地说话。

She was so nervous that she started ___mumbling during her speech.