To this question,the professor provides the explanation that
1个回答

应该去掉,但楼上的说那是插入语不妥,the woman with fur collar是非限制性同位语,指前文的portrait(同位语从句的主语).

that是连词,引起后面整个作同位语从句,用以解释和说明explanation的具体内容,本身不作成分,其后面的portrait是主语.