1/ Thanh works harder now than last year.

-> Last year Thanh didn't work as hard as he does now.

2/ He doesn't understand the lessons as well as last year.

-> Last year he understood the lessons better than he does now.

3/my sister usually gets up earlier than me.

-> I usually get up later than my sister.

4/ Yesterday, Mr Pike didn't drink as much as Mr White.

-> Yesterday Mr White drank more than mr.pkie