GMAT Sentence Correction (SC) | Re: Ants, by themselves, are weak creatures,

A. when ants are considered along with others of their species,

B. when considering them with others of their species, then
"then" is redundant. I believe "then" is used for expressing the effect of a cause. But here, there's no cause-and-effect statement. Hence, the use of "then" is wrong.

C. ants, when considered with others of their species,
This option will make the "they" in the non-underlined portion redundant.
D. considering them with others
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