This is a combination of cause-effect and assumption
Presence of the nerve-growth inhibitors is the cause behind damaged nerves not regenerating themselves (effect).
Now we have the antibodies developed, we can use the antibodies to remove the cause and possibly no cause no effect.
The assumption in making the conclusion that"nerve repair will be a standard medical procedure" is that if you switch off the inhibitor button, there are no alternate effects.
Option A challenges this assumption by highlighting that if we switch off the inhibitors button there can be significant issues, thus making us believe less in the conclusion that "standard medical procedure".
Option B says certain and not all. More importantly, as Karishma pointed out, similar doesn't mean the same. Even one difference can make a difference.
Option E says it would require steady supplies - there is nothing in the argument that says supplies can be a challenge. This is at best out of scope - the argument scope is limited to that "nerve repair will be a standard medical procedure" how - using the antibodies that deactivate those inhibitors.