Hello Everyone!

This looks like a great example of a question that focuses on parallel structure! Whenever we see a question with a long list, parallelism is a great place to start narrowing down wrong answers.

Let's break down each answer to rule out answers that don't use parallel structure. We know that every item in the list has to be parallel to the one item on the list that isn't underlined: "ward off." Since we cannot change that part, we need to match all other items in the list to that!

A. Mars would have to endure low levels of gravity for long periods of time, avoiding large doses of radiation, plus contending --> NOT PARALLEL
B. Mars would have to endure low levels of gravity for long periods of time, avoid large doses of radiation, contend --> PARALLEL
C. Mars, having to endure low levels of gravity for long periods of time, would also have to avoid large doses of radiation, plus contending --> NOT PARALLEL
D. Mars, having to endure low levels of gravity for long periods of time, avoid large doses of radiation, plus contend --> PARALLEL
E. Mars, who would have to endure low levels of gravity for long periods of time, avoid large doses of radiation, contend with --> PARALLEL

We can rule out answers A and C for lacking parallel structure!

Okay, so this narrows things down a bit! Let's break down any other problems with answer B, D, and E:

B. Mars would have to endure low levels of gravity for long periods of time, avoid large doses of radiation, contend

This is CORRECT! It uses parallel structure and includes a verb to make this a complete sentence.

D. Mars, having to endure low levels of gravity for long periods of time, avoid large doses of radiation, plus contend

This is INCORRECT because by adding the comma and changing the verb to the gerund "having," this is now just one long run-on sentence. It is missing a verb!

E. Mars, who would have to endure low levels of gravity for long periods of time, avoid large doses of radiation, contend with

This is also INCORRECT because the comma turns this into a long run-on sentence that is missing a verb.


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