5.May I go home? No,you ___ (mustn't) 為何can't不行 6.He fell off a bicycle and ___ (was hurt) 為何hurt不行 感謝!!!?

5. May I go home? ("may" is modal verb to ask permission)
To answer no to deny permission, we must use the modal "must not" to express prohibition. The negative form of "can" is only used to express ability or possibility.

6. He fell off a bicycle and was hurt. (hurt is adjective to mean injured)
We cannot use the verb form of hurt alone without any object.
- He hurt himself.
- He hurt his back / leg / head. (part of the body)

** hurt can be used intransitively but it means your part of body (the subject) feels pain (e.g. my head hurt)

如果第一句要回 cant 那 前面問句就要視 can i go home ? 第二句 因為 是被動式吧 因為跌倒了所以被受傷了 而不是 受傷地方主動去受傷的 以上是我自己想法