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.

20世纪40年代（）发现，作物生长发育要求一定的昼夜温差即所谓（）。