题目

When it comes to your skin, there is an important fact that you must keep in mind: Your skin is the largest organ of your body．As an obvious result, skin health and maintenance（保养） is vital．Your skin does everything from protecting you from the elements to assisting you with breathing．Your skin keeps your body hydrated （含水的） and regulates your body's temperature．In the end, this really is only the beginning of all of the various vital functions that your skin provides to you． Despite the extreme importance of a person's skin, the reality is that many people simply d12．Miss Black is a friend of ________，she always looks after my sister．（　　）A．Mary's mother'sB．Mary's mother'C．Mary mother's