Problem with a student's file

I am unsure how to make this file printable on my 3D Printer. Can someone help me with this file, please?
du ar en jordgubbe.skp (271.3 KB)

The larger part has internal structures and faces not visible to the outside that make it impossible for an outsider to understand what can be cleared and what is to remain.

@Anssi shows much of what is wrong with the larger piece. There’s also reversed faces.

Compare my version of the thing to the student’s.
du ar en jordgubbe fixed.skp (208.0 KB)