Explanation : They in choice (a) means 'some of our ruling politicians' (the subject). Also grammatically`they have a right to plunder........' is correct wheras'........right to the punder ........' is incorrect.
Explanation : (b) The expression must be " it is of cardinal importance". (c) There is no urgency in understanding, "It should be understood" is enough. (d) Instead of "it cannot be,' the expression should be it must be'. So choice (a) is the best, It is important that the two things are not to be interfered with.