为什么Jack hurt his back playing volleyball中的play用的是ing形式而不是过去式?

Jack hurt his back playing volleyball.为什么用palying?什么语法? 为什么Jack hurt his back playing volleyball中的play用的是ing形式而不是过去式? Jack hurt his hand ( )play volleyball.用to play还playing答案是playing,为什么不能用to play Jack hurt his arms in a car accident yesterday.改为一般疑问句 Jack fell ____ and hurt his leg.off down behind选择哪个? Jack ______ (hurt) his ankle last month and he ______ (have) to walk with crutches now. His leg hurt还是hurts补充一个：His legs hurt 还是hurts,为什么? The _____to his feeling is more serious than the___in his body.A.pain;hurt B.ache painC.ache;hurt D.hurt;hurt 为什么? he--- (hurt)his foot badly 为什么不用hurts He hurt his leg 他的腿受了伤 hurt为什么后面不加s 一道七年下英语题Jim _____(hurt) his arm yesterday.And his arm _____(hurt) now.怎么填?为什么? on his way to the hill jack fell down.He hurt his handsand knees,jimmy got to the top all right.c(ccompound sentence so sharply----------that he couldn't eat anything A did his teeth hurt B was his teeth hurt为什么b不对,好像也可以说 his hurt was hurt sharply Jack hurt himself very badly译成汉语 my ear is hurts ,his arm hurt .为什么前面一个hurt 要加 s ,而后面一个不用加 Every Jack has his Every jack has his A fire fighter _____by burning wood that fell on his back.A was hurt.B.hurt .为什么选A.hurt不是可以用主动表示被动么.