Complete the sentences.1.this is a bookcase.-these . window.-.3.this is a .that is a blackboard.-these a table.-

1. These are bookcases.
2. That is a window.- Those are windows.
3. This is a door. - These are doors.
4 That is a chair. - Those are chairs. 
5. This is a blackboard. - These are blackboards.
6That is a table. - Those are tables.