Here's the solution.
a. should have permanently revoked licenses --> This means that drivers with more than 3 convictions for drunk driving will already have 'permanently revoeked licenses' i.e. having a permanently revoked license is a pre-requisite for people with more than 3 drunk driving convictions. This clearly not what the sentence should mean. Hence incorrect.
b. should have a permanently revoked licenses --> This has a similar meaning as that of option A alongwith the additional error of having 'a' (used with singular objects) before the plural object 'licenses'. Hence incorrect.c. should have their lincenses permanently revoked
--> This sentence is correct as it means that those drivers who have more than 3 drunk driving convictions will have their licenses permanently revoked by the authority thereby stopping them from driving irresponsibly again.
d. are to have revoked their licenses permanently --> This means that drivers with more than 3 drunk driving convictions should get their licenses permanently revoked from the authority. This is simply absurd. (Who would want to get this done on purpose? :D )
e. are to have permnanently revoked license --> Singular object 'license' does not agree in number with the plural subject 'drivers'. Hence incorrect.
Hope this helps.
MBA Candidate 2015 | Georgetown University
McDonough School of Business