AbhiS, good to see you back on this post
Ok, I will put light on my understanding; For that, I will break the sentence:
---
Historians have universally accepted
Dark Ages --> "Historians" is the subject and "Dark Ages" is the object
Now, we know that we use "which with comma" to introduce a non-essential modifier. For example: I bought a car
, which is of red color.
Similarly.. "which is a term used ....... of Renaissance" is a modifier to the nearest legitimate noun "Dark Ages" and yes it is correct in SVA. Now, if we are trying to introduce a "which with comma" modifier between the sentence then we need to end it with a comma.. that is what has been done by comma
"Renaissance, and ", meaning modifier is over.
A similar example can be: A box of nails
, which is kept on table, is of Red color.. here, the modifier "which is kept on table" is introduced between the sentence by using "which with comma" and is ended with "comma"
Now, on the same example, if we remove the modifier ... the sentence becomes: A box of nails is of Red color
Similarly, now going back to original question's part {C}:
Historians have universally accepted Dark Ages
, which is a term used to denote the entire period between the decline of Roman Empire and the starting of Renaissance, and are characterized by decline of human standards, both cultural and economical
can be re-written without modifier as:
--- Historians have universally accepted Dark Ages and are characterized by decline of human standards
Now, we know "Historians" is the subject of the sentence... So, we can re-write as:
Historians have universally accepted Dark Ages
Historians are characterized by decline of human standards --> Doing so impacts the meaning of the sentence.. as "historians" are not characterized ... So we must eliminate this answer choice
Aside, yes the most important construct is X,Y and Z.. but we can have many combinations to this:
For example:
X
, which is A,B and C, Y
, which is M,N and 0, and Z
, which is W, X and Y.
wherein "which + comma" is used to embed non-essential modifiers.
Regrets for the long post.
Cheers!