if he could take part in the competition next week

前提条件是他腿受伤了，不能参加比赛。
后面就出现了一句 he would win the 400 race competition if he could join the competion next week.
而且这句话是在讲完虚拟语气后面的练习出现的。也就说考察的是虚拟语气表将来的情况。if虚拟语气与将来事实相反，不就是should+do，were to do，或者动词过去式吗，那这儿为什么答案是给的could join呢？读起来倒是挺通顺的，表示能力嘛。可以参加的话。但是这是if的从句哦。又不是主句，从句表将来只会出现should这个情态动词。那些could might would 都只会在主句中出现，不是吗？有没有人能给个详细的解答
就算是于现在事实相反，从句也不会出现could。除非它没用虚拟

表示与事实情况相反 条件从句的谓语形式 主句的谓语形式
表示现在情况 过去式(did)
(be常用 were) Would / could / might / should +动词原形(do)
表示过去情况 过去完成式(had +done 上面4个情态动词+have done
表示将来情况 ①过去式 (did)
②should + do Would / could / might / should +动词原形(do)
③were to do 4个情态动词 + do
而且这里明显又next week 说明是将来的情况。将来相反：

I asked him 后面是跟if he can 还是if he could? could you tell me if he _____to Paris? Anders thought as he stood there that if Baard could afford to give forty dollars he could too “He wondered if he had bitten off more than he could chew" what's meaning? I could not put someone in his place even if he needed it would ,if...could 语句 If could be worse if you had told us earlier who he was,we could have introduced him at the meeting. if i could turn back If only I could fly.