Yesterday my class teacher…….of my friends,,,,,classmates.
‘That’ denotes a distant thing, person or an object whereas ‘this’ denotes proximity or nearness. In relation to time too ‘that’ means ‘distant time’ or ‘past time’ or ‘time that has already gone or elapsed.’ ‘This’ means ‘present time’ or ‘now’. e.g.
The teacher said to the student,”Last week too you were absent. At that time I did not punish you. But this time I shall not spare you.”
It is ample clear now. Nevertheless for any query you are always most welcome.