Sir~speak up a bit 老师大点声！

Speak up - to speak in a louder voice so that people can hear you

例如：

1.Could you speak up? We can't hear at the back.

你能大点声吗？我们在后面听不到

2.If you thought that wasn't fair,why didn't you speak up?

如果你认为那不公平,为什么不大胆说出来?