Symbiosis National Aptitude Test SNAP 2017 Paper

The phrase, 'desirable that' is followed by the present subjunctive form, i.e., the base form of the verb. So, 'furnish' will be correct here.
Option b is ruled out as it uses the m odal 'should' (obligation) which is not needed in this context; c is ruled out as 'it is highly to be desired' is an incorrect expression; d is ruled out as 'should'(obligation) and 'have to'(necessity) are separate modals that give confusing sense if used together.