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Is this / these your exercise-book ?
No, it isn't . Thas is /These are my  exercise -book. It is green .
This  is / These  are my scissors , and thas is / those are  her pictures .
This / These  aren't  your pensils. They are my pencils .
Are this / these  your cassettes ?
No.  Those / That are my cassettes in that / those bag.