It is believed that part of animals can’t stay alive in water at 1,500 meters below ____ sea level.
Earth is believed ______ by an object the size of Mars at some point in the distant past before its surface cooled.
With temperature ______ so rapidly, we could not go with the experiment.
--- Is John in the office? ---I didn’t see ______ there.
Because of ______high demand for Type AB blood,____supplies of it are usually limited.
His parents never approve of_____ he plans to do, which always annoys him.