问题补充：
Im sorry to tell you that I on the play ground.
A. forget your books
B. forgot your books behind
C. have left your books alone
D. left your books behind
答案：
A. forget your books
B. forgot your books behind
C. have left your books alone
(答案→)D. left your books behind
解析：句意：对不起我要告诉你的是我把书忘在了操场。这里forget是忘记的意思，但是后跟地点状语时，不能用它，而用leave sth behind走后留下某物。leave sth alone不去理会某物；根据语境忘记书是在过去，故选D。
