* Un-", "in-", "non-: These prefixes can be attached to many words to create the negative form. For example, "unbreakable", "incomprehensible", "nonexistent".
* Impossible: This word directly conveys the meaning of "which cannot be".
* Unattainable: This word implies that something is beyond reach or cannot be achieved.
* Improbable: This word suggests that something is unlikely or has a low chance of happening.
* Prohibited: This word indicates that something is forbidden or not allowed.
To provide the best answer, please provide the sentence or context where "which cannot be" is used.