Use a or an

  1.  This is pencil.

  2.  He's doctor.

  3.  Sue eats apple.

  4.  Tennis is game.

  5.  I see old book.

  6.  He is teacher.

  7.  She is pupil.

  8.  He's got orange.

  9.  It's good bike.

  10. She's girl.