Sentence Correction: Comparatives - Superlatives

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.

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.

This answer choice is grammatically incorrect because of its repeated misuse of the Superlative form indicated here by the use of the word most. Most must be preceded by the word the. In this answer choice, however, most difficult is preceded by a.

Although this answer choice corrects the original Comparative error by defining the group being compared (all engineering challenges), it is grammatically incorrect. The verb carry requires a preposition in order to correctly connect to multiple tasks. One does not carry multiple tasks - one carries out multiple tasks.

Whenever the first verb requires a preposition after it and the second verb does not, the preposition must not be omitted:

Incorrect: John cares and loves Jane.
Correct: John cares for and loves Jane.

What helps us identify this question as a Split Construction question and identify the mistake is the following Stop Sign:

A split construction: Verb A + and/or + Verb B + object

Although this answer choice corrects the original Comparative error by defining  the group being compared (all engineering challenges), it creates Redundancy with the wordy phrase an environment that is both dynamic and unpredictable.

Excellent!

This answer choice corrects the original Comparative error by defining the group being compared (all engineering challenges).

out and coordinate multiple tasks simultaneously while operating in a dynamic and unpredictable environment, is the most difficult engineering challenge
out and coordinate multiple tasks simultaneously while operating in an unpredictable and dynamic  environment, is a most difficult of all engineering challenges
and coordinate multiple tasks simultaneously while operating in a dynamic and unpredictable environment, is the most difficult of all engineering challenges
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
out and coordinate multiple tasks simultaneously while operating in a dynamic and unpredictable environment, is the most difficult of all engineering challenges

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