The doorbell had been ringing for several minutes before it ______.

A answered       B had answered          C was answering       D was answered

临床上某护士将含乙醇、甘油的氯霉素注射液加入5%葡萄糖注射液中，出现了沉淀。该护士向药剂科人员咨询产生沉淀的原因，药师的回答正确的是（）

A.注射液溶媒组成改变

B.电解质的盐析作用

C.注射液pH改变

D.直接反应

E.发生聚合反应