The condition that causes weak / brittle bones from calcium deficiency is known as A) osteoporosis.
Many elderly people suffer from osteoporosis and that is why a fall as an older person may result in a broken bone. If a younger person had the same fall, their bones are not as likely to break.
Crohn's disease is a condition in the intestines in which the person suffers from chronically inflamed bowels. Celiac disease is the disease in which a person suffers great pain and cannot properly digest foods with gluten. Hemophilia is a blood disorder in which a person could bleed a lot from a small cut because the blood does not clot like the average person's blood does.