Moviegoers know that any special effects are reeled by computers. _____ they often don't know is that these scenes still require a lot of work.
A、That
B、Whom
C、What
D、How
【正确答案】：C
【题目解析】：they don't know后面缺少宾语，能在从句中充当宾语的只有whom和what，根据句意可知只能选what。句意：看电影的人都知道，任何特效都是由电脑控制的。他们通常不知道的是，这些场景仍然需要大量的工作。
