Washing hands thoroughly is one of the effective ways to avoid ________ by virus.
I was in the baths , ______ I didn’t hear the telephone, which was ringing several times.
She was so _____ in her job that she didn’t hear anybody knocking at the door.
Our professor told us that salt water _____ at a lower temperature than fresh water.
Until recently historians assumed that calendars ________ with the advent of agriculture.
. ________ when the boulders suddenly disappeared.