硫酸镁+碳酸氢钠

A．pH值改变产生沉淀
B．水解产生沉淀
C．生物碱盐溶液的沉淀
D．复分解产生的沉淀
E．氧化产生的沉淀对下列药物溶液产生浑浊或沉淀的机理进行分析：

—What about your TEFL test?

—I have answered all the questions, but I’m not sure _____ I could get a high enough score. 

A．what

B．if

C．when

D．why