Complex sentence: When Bart complains he never gets any mail, Marge gives him the family's junk mail, one piece contains a credit card application, which he fills out under the name of his dog Santa's Little Helper.
Split into simpler sentences: When Bart complains he never gets any mail, Marge gives him the family's junk mail. One piece contains a credit card application, which Bart fills out under the name of his dog Santa's Little Helper.