Translation:The farmer has two cows on the farm.
I would only say "...on the farm". "at" sounds temporary but "on the farm" includes the cows in the whole running of the farm.
Thanks! Here's where my non-native English leaves me grasping.. Umm -Perhaps nice for the non-native English speakers to include it as a less-desirable alternative? (Clearly I'm a desperate, grade-grubbing student:-))
I understand that the correct preposition is "on", but maybe "in" could be marked as a typo rather than an error.