Дуже потрбно! Даю 20 балв! Fill in the blanks with a/an

Дуже потрбно! Даю 20 балв! Fill in the blanks with a/an or the .
1) This is ... ball.The ball is blue.
2) There is ... cosy sofa in my room. There are two nice pillows on ... sofa.
3) It is ... computer ... computer is on the desk.
4) There is one big window in my room. There are many flowerpots on ... windowsill.
5) There is ... table with four chairs in ... middle of my room ... vase with flowers is on table.