___ most of the earth’s surface is covered by water, fresh water is very rare and precious

I am concerned ____ it that I can’t concentrate ____ my work because of headache

John has really got the job because he showed me the official letter_____ him it.

If I can help________，I don’t like working too late into the night.[ ]

Making _______ good impression on the interviewers isof ________ vital importance.