内表面常有防止血液倒流的瓣膜的是（　　）

A．大动脉

B．小动脉

C．静脉

D．毛细血管

The nurse is working in a support group for clients with acquired immunodeficiency syndrome (AIDS). Which point is most important for the nurse to stress（）

A. Avoiding the use of recreational drugs and alcohol.

B. Refraining from telling anyone about the diagnosis.

C. Following safer-sex practices.

D. Telling potential sex partners about the diagnosis, as required by law.