医生告诉他，这种神经损伤是不可逆的。

The doctor told him that this nerve damage is ___irreversible.

这种化学变化是不可逆的，一旦发生就无法还原。

This chemical change is ___irreversible and cannot be undone once it occurs.

这种化学物质会造成不可逆转的环境污染。

This chemical causes ___irreversible damage to the environment.