--Is it _____ pen? --Yes. It' s ______ orange pen. A a; a B. an; an C. a; an D. an; a
—Is your brother at home? —No. He ________ the library. He hasn’t come back yet.
We know that about seventy percent _____ the earth _____ covered by water.
you drive,you will be.
The policeman asked the child ________ cross the street ________ the traffic lights turned green.
— I have great _______in finishing the work by myself. Could you help me? — No problem.