_____ the great teacher Zhang Lili was in hospital, many people hoped she would get better soon.  [ ]

A. If            

B. Until          

C. Before          

D. After

灼烧残渣只近似地表示溶解固形物中矿物质的量（称矿物残渣）。所谓近似表示是因为在灼烧时，除发生有机物被烧掉和残存的湿分被蒸干外，还会发生（），结果使得残渣的成分发生了变化。