At first, I didn’t know what ____ Facebook was, and now I do know what it is. I have to say, it sounds like ____  huge waste of time.

A．/; the

B．/; a

C．the; a

D．a; the

部分工作人员应学会触电、窒息急救法与人工呼吸，并熟悉有关烧伤、烫伤、外伤、气体中毒等急救常识。