When the boss entered the room, the workers were pretending ____ hard at their machines.
A . to work B . to be working C . to have worked D . working
B
【详解】
考查不定式的进行时。句意:当老板进来时,员工们假装正在机器上努力的工作。本题考查短语 pretend to do sth 假装做某事,结合句意可知 “假装工作”的动作正在发生,故用不定式的进行时 to be doing ,故选 B 项。