关于股骨骨折，哪种说法不正确（）

A.老年人身体弱，不宜手术治疗

B.陈旧性骨折严重成角畸形，早期可手法折骨，再按新鲜骨折处理

C.最理想的治疗方法是闭合插针

D.3岁以内的儿童均可采用垂直悬吊牵引

E.儿童股骨干骨折1～2cm重叠可减少双下肢的长度差异

Wei Zhang has funds on deposit with Iron Range bank. The funds are currently earning 6% interest. If he withdraws $15000 to purchase an automobile, the 6% interest rate can be best thought of as a(n) :（）

A. discount rate.

B. required rate of return.

C. opportunity cost.