下列化学实验操作中，正确的是（　　）

A．为节约药品，实验用剩的药品要放回原瓶

B．给试管里的药品加热时，先进行预热

C．蒸发结晶时，待水分全部蒸干后再移走酒精灯

D．为防止液体外溅，胶头滴管要伸入试管内滴加

I can't tell you the exact time I'll get there, maybe at eight or nine or even later. ____,

I'll be there as early as I can. [ ]

A. Anyhow

B. However

C. Thus

D. Therefore