He said that not until the heavy snowblocked the express ______ how serious the weather was

“Tommy, run! Be quick! The house is on fire!” the mother shouted, with clearly in her voice.

The house could fall down soon if no one ______ some quick repair work.

It is the prevention of disease_____ itssuccessful treatment that has led to the rapid increase of the world’spopulation.

It was _______ back home after the experiment.