Translation:They have cut the trees
2 CommentsThis discussion is locked.
Not really. Some sources say that the inclusion of an object prefix indicates definiteness or specificity of the object, but there seems to be some variation and there is no consensus. At least for some speakers, it is simply optional.
In any case, the way this course is taught, it is optional and so this should either be accepted or the course content changed a bit to reflect this distinction. If you see it again, report it.