The professor spoke in a loud voice ______ every one of us could hear him.

We recognized his voice ______ he spoke on the radio.

A．while

B．after

C．in case

D．the moment

We recognized his voice ______ he spoke on the radio.

A．after

B．in case

C．the moment

D．while

We recognized his voice ______ he spoke on the radio.

A．after

B．in case

C．the moment

D．while

He spoke in such a high voice ______ at the farther end of the room.

A．as to be heard

B．to be heard

C．as to hear

D．to hear

The professor spoke very clearly to make himself ______.

A．to understand

B．understood

C．understanding

D．understand

All students in the class ______ a loud laugh when the professor told them a joke.

A．let up

B．let down

C．let off

D．let out

All students ______ a loud laugh when professor Henry Mitchel told them the joke.

A．let off

B．let down

C．let out

D．let up