A：AlCl3
B：Ca(HCO3)2
C：NaAlO2
D：Na2SO3
—Which is more useful, reading or writing?
—I think _______ of them are useful.
如果要培养细菌和真菌，接种前培养皿、培养基必须经高温处理，这是因为（ ）
——What do you want to be when you graduate from middle school?——I want to be _________university student. I'm in great ______ need of knowledge.
