Sentence Correction

Robotics engineers are discovering that creating a machine that can carry out and coordinate multiple tasks simultaneously while operating in a dynamic and unpredictable environment, is the most difficult engineering challenge.

A. out and coordinate multiple tasks simultaneously while operating in a dynamic and unpredictable environment, is the most difficult engineering challenge
B. out and coordinate multiple tasks simultaneously while operating in an unpredictable and dynamic environment, is a most difficult of all engineering challenges
C. and coordinate multiple tasks simultaneously while operating in a dynamic and unpredictable environment, is the most difficult of all engineering challenges
D. out and coordinate multiple tasks simultaneously while operating in an environment that is both dynamic and unpredictable, is the most difficult of all engineering challenges
E. out and coordinate multiple tasks simultaneously while operating in a dynamic and unpredictable environment, is the most difficult of all engineering challenges

[spoiler]OA: E.[/spoiler] The reason why choice A is incorrect is given as follows: This answer choice is grammatically incorrect as it misuses the Superlative form indicated here by the use of the word most. The Superlative form requires that the group under comparison be defined. However, this answer choice does not provide information about the group of which the challenge is the most difficult.
In order for this Superlative to be complete, this group must be defined.

My doubt: Why do we need to define this group to complete the superlative?

It is correct to say: Aishwarya Rai is the most beautiful woman in the world. This actually means Aishwarya Rai is the most beautiful of all women in the world.

[spoiler][/spoiler]

Valid Doubt.. I ended up with A, when left with A/E

Experts please help!

B uses "a most difficult..." which does not make sense.

C drops the "out" which we need with "carry"

D uses "an environment that is both dynamic and unpredictable," which is overly wordy.

We can get to A and E pretty easily.

I actually don't like either of them. They both end with ", is the most difficult engineering challenge "...where does that comma come from?

I think the group is defined as "engineering challenges" in A, so I don't see a problem there.

What is the source of this question?

I got this question in the free MasterGMAT test.

(A) for me.