Mary and John____ each other since childhood.

Mary and John____ each other since childhood.
A、have been knowing
B、knew
C、have known
D、had known
【正确答案】：C
【题目解析】：【考点点击】本题考查现在完成体。【要点透析】现在完成体表示过去某一时刻发生,且延续到现在的动作或状态,强调对现在造成的影响,常与表示一段时间的状语连用。表示一段时间的状语有trr“达…之久”, since“自从…以来”, in the last few years""“在最近几年”。know是延续性动词,且句中无“过去的过去”的含义,故选C。