问题补充：
单选题Whilewewererunningontheplayground,Jacksuddenlystopped___________andlayontheground,soweallstopped___________whatwaswrongwithhim.A.running; to seeB.running; seeingC.to run; to seeD.to run; seeing
答案：
A解析stop doing sth，停止做某事，stop to do sth停下来去做某事
