Mrs. Cray, an African American, is admitted to the hospital after sustaining a hip fracture. She is 5 ft. , 4 inches tall and weighs 96 lbs. She has five children and has used estrogen replacement therapies for 10 years. She told the nurse that she "just stepped forward and fell. " The results of her bone density tests indicate she has osteoporosis. Which of the following is the greatest risk factor for osteoporosis for this woman()

A. Her long-term use of estrogen.

B. Her weight.

C. Her family.

D. Her race.

教师在指导学生完成作业要做到（）

A.指导学生审题

B.指导学生做题

C.指导学生检查作业

D.指导学生自我提高