— Oh I forgot _______.

A.turning it offB.turn it offC.to turn it offD.having turned it off

【答案】C

【解析】

考查固定短语。句意：—办公室的等还在亮着。—哦，我忘了要关灯了。固定搭配forget to do忘记要做某事，forget doing sth.忘记已经做过的事情。turn off关掉，根据“The light in the office is still on.”可知，忘记要关灯了。故选C项。