Its easier to start with the second blank Scrutun defends classical vernacular against its critics so option E closely matches with this.
wherears is a keyword that need to be noticed.It is a transition word so it is opposite of the previous sentence so pick a negative word Affront .
Now it is easy to fill the first blank it states that need for genis and tradition should be root of our understanding so centre can be a good choice .


IF YOU LIKE MY EXPLANATION.PLEASE GIVE KUDO's.I'm hoping to take practice tests.

Without the need for genius and with tradition placed at the (i)____ of our understanding of what architecture is, Scruton gives a critical appraisal of the classical vernacular, defending it against its (ii)___ and regarding its merits when set beside the legacy of modernism. The good manners of the classical pattern book provide guidance for the educated builder, whereas the extravagant intellectualism of the would-be modernist genius is a(n) (iii) ____ to any who would live in an educated community.

it is easier to start with 3rd blank. "Whereas " represents contrast. so part before whereas is positive hence after this it should be negative in idea. so only negative word is AFFRONT.
Now for 2nd blank, person is defending against. It is obvious that he will defend against some bad persons or those who do not believe. Hence DEFRACTORS

for 1st blank, Fringe and borderline are synonyms so both are out. hence CENTRE is the answer
QED BEI is the final answer

Without the need for genius and with tradition placed at the (i)____ of our understanding of what architecture is, Scruton gives a critical appraisal of the classical vernacular, defending it against its (ii)___ and regarding its merits when set beside the legacy of modernism. The good manners of the classical pattern book provide guidance for the educated builder, whereas the extravagant intellectualism of the would-be modernist genius is a(n) (iii) ____ to any who would live in an educated community.

You cannot give a critical appraisal of the anything and also defend it without placing it at the centre of our understanding.Definitely not at the fringe or the borderline.

You defend anything against its detractors and not its devotees or patrons.

The author has defended the classical vernacular regarding its merits when set beside the legacy of modernism. So he is biased towards the classical vernacular. And the word "whereas" in the last sentence contrasts the good manners of the classical book which provides guidance to the educated with the extravagant intellectualism of the would-be modernist. Such a contrast would be meaningful only if there is a negative judgment on the would-be modernist and his extravagant intellectualism, and these are depicted as failing to provide guidance to the educated community. Thus affront would be the right choice for the third blank. The words "extravagant" and "would-be" themselves suggest a negative mood.