CR pregnant women

What the...? I do not understand the answer for this one!

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Many pregnant women suffer from vitamin deficiency, but this is frequently not due to vitamin deficiency in their diets; most often it is because they have higher requirements for vitamins than do the rest of the population.

The best criticism of the reasoning in the statement above is that it

(A) fails to specify the percentage of pregnant women who suffer from vitamin deficiency. Irrelevant

(B) gives insufficient information about why pregnant women have higher vitamin requirements than do other groups. Irrelevant

(C) fails to employ the same reference group for both uses of the term "vitamin deficiency." Correct. This is ambiguous. If they have higher requirements for vitamins, their diet would be lacking in vitamins otherwise.. why would they be deficient? The context for 'vitamin deficiency' as applied to pregnant women is different from the one that's applicable to their diets (which is the standard for the rest of the population)

(D) provides insufficient information about the incidence of vitamin deficiency in other groups with high vitamin requirements Irrelevant

(E) uses "higher requirements" in an ambiguous manner.Incorrect. Higher requirements for vitamin intake is is compared to the rest of the population, and should suffice

IMO: E
...
(C) fails to employ the same reference group for both uses of the term "vitamin deficiency."false, as the pronoun "their" clearly refers to "Many pregnant women"
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Many pregnant women suffer from vitamin deficiency - vitamin deficiency: the organism requires more vitamins than it has.
vitamin deficiency in their diets - what does "vitamin deficiency" mean here? or refer here? Clearly, there is other "vitamin deficiency" that applies for diets.