thanks Rich
for this info. honestly it never occurred to me that "Yo-yo Ma" is human !! but anyway i still feel that is it not wrong to say that a "versatile style" employs aspects of genres as varied as Baroque
i mean how can "style" employ something ?

Yo-yo Ma, whom according to the classical cellists of the world is perhaps the world's best, plays in a versatile style which is ever-changing but which also employs aspects of genres as varied as Baroque, American bluegrass, and modern minimalism.

Lets separate as clauses:
Removing the modifier which is enclosed in comma pair.

Yo-yo Ma plays in a versatile style which is ever-changing but which also employs aspects of genres as varied as Baroque, American bluegrass, and modern minimalism.

It doesn't make sense that style can employ X, I still think YYM employs X.
Even if that is case , I will prefer

Yo-yo Ma plays in a versatile style,which is ever-changing but which also employs aspects of genres as varied as Baroque, American bluegrass, and modern minimalism.

2nd Which is not required and also second part of the sentence is acting as modifier modifying the style.

A) whom according to the classical cellists of the world is perhaps the world's best, plays in a versatile style which is ever-changing but which also employs

I think style cannot employ .. Hence Incorrect.

B) considered perhaps the world's best by the classical cellists of the world, plays in a versatile style, which at the same time employs

I think style cannot employ.. Hence Incorrect

C) regarded by the world's best classical cellists as the best cellist of the classical world, plays in an ever-changing style, yet employs

perfect - I think this is the OA.

D) looked on by the classical cellists of the world as perhaps the world's best, who plays in an ever-changing style all his own, which also employs

If we plug in the sentence fragment:

The sentence becomes :

Yo-yo Ma,looked on by the classical cellists of the world as perhaps the world's best,who plays in an ever-changing style all his own, which also employs

We can remove the modifier inside the comma pair, the sentence becomes:
Yo-yo Ma who plays in an ever-changing style all his own, which also employs
There are two subjects in the same clause - Incorrect.

E) whom the world of classical cellists looks on as the best, plays in a versatile, ever-changing style while at the same time employing
"Employing" is not verb, it should make sense with the subject. It requires an auxiliary verb "is" or "was". Incorrect.

What is the OA?

aditya8062 wrote: my doubt: "which" in B seems to refer to "versatile style" ,when it should be referring to "Yo-yo Ma"

Yo-yo Ma's versatile playing style employs aspects of genres as varied as Baroque, American bluegrass, and modern minimalism.
One definition of to employ is to make use of.
Here, the conveyed meaning is as follows:
Yo-yo Ma's versatile playing style MAKES USE OF aspects of genres as varied as Baroque, American bluegrass, and modern minimalism.
This meaning makes sense.

Is the answer E?

I actually am the author of this question so perhaps can shed some light.

Mitch is correct that my intention was to use the word "employs" as "make use of" and not "gives a job."

Since Yo-Yo Ma is described as the "world's best" it should be implicit that this is a human being (note the capitalization as well).

The correct response is (B). This is by no means a "perfect" sentence (and is a bit wordier than we might hope), but it is grammatically correct. It also avoids the problems in meaning contained in the other options.

In (A), "whom" is used incorrectly. You use "who" when you are referring to the subject and "whom" when you are referring to the object. Since "Yo-yo Ma" is clearly the subject, "who" would be correct. Additionally "ever-changing" and "versatile" are redundant.

(C) has some issues with meaning. The "classical world" is somewhat unclear, and since we know Yo-yo Ma plays in a variety of genres, including "modern minimalism," it's clear that is not the intended meaning of the sentence. In addition, the word "yet" implies a contrast, but the Yo-Yo Ma's versatility is exemplified by the list of genres in which he plays. The two ideas are not meant to disagree.

In (D), this is a sentence fragment. Each of the three dependent clauses describe the subject, "Yo-yo Ma," but we are never given a predicate verb to make the sentence a complete thought.

In (E), as with (A), "whom" is used incorrectly. Only "who" can take the place of a subject. Additionally, "every-changing" and "versatile" are redundant.