He feels very excited and his heart ________ very fast．
A.is strikingB.is beatingC.is hittingD.knocks在线课程B
strike, beat, hit, knock都有“敲；打”的意思。strike强调用木棒、石头等的“打”，与hit用法接近；beat侧重“连续的敲击”，如：The raining is beating against the window．beat也可以指“心脏的跳动”；knock强调“用力撞击”，如“将某人撞倒”可以说knock sb．down。