单词学习：mutter 动词
mutter
/ˈmʌtər/
咕哝，低声抱怨，含糊不清地说
The student began to mutter under his breath after 顾老师 corrected his mistake.
在顾老师纠正了他的错误后，那个学生开始低声咕哝。
单词卡片
卡片已就绪
