When you have a lesson e.g. about this/that , these/those , it would be a good idea to mix the exercises a bit more . Don't just make a set of 18 questions only with "this", and then another set of 18 questions only with "that". otherwise our brain gets used to translating everything with "this" for the duration of the whole exercise and doesn't think about the word anymore . if you mix "this" and "that" in one exercise, we will have to pay more attention when we translate and the difference between the two words "this" and "that" will become clearer to us