This question is primarily testing LOGICAL MEANING. Whenever language about percentages or proportions appears on SC or CR, we want to ask ourselves: "what is this the percent *of*? Is it logical and unambiguous?"

(A) In California today, Hispanics under the age of eighteen account for more than 43 percent, compared with a decade ago, when it was about 35 percent.
- 43% of what? Is it that under 18 yr olds account for 43% of Hispanics? Or of Californians overall? Or of Californians in this age range? Completely unclear.

(B) Of the Californians under the age of eighteen, today more than 43 percent of them are Hispanic, compared with a decade ago, when it was about 35 percent.
- here we've fixed the ambiguity: we know that 43% is the proportion of Californians under 18 who are Hispanic.
- however, "of them" is redundant when we've already specified "of the Californians..."
- the "it" is somewhat ambiguous

(C) Today, more than 43 percent of Californians under the age of eighteen are Hispanic, compared with about 35 percent a decade ago.
- clear and unambiguous proportion
- clear and parallel comparison btw 43 and 35

(D) Today, compared to a decade ago, Californians who are Hispanics under the age of eighteen account for more than 43 percent, whereas it was about 35 percent.
- again, 43 percent of what?
- the "compared to" is awkwardly placed - it's not clear that the 35% was a decade ago
- same "it" issue as in B

(E) Today, Hispanics under the age of eighteen in California account for more than 43 percent, unlike a decade ago, when it was about 35 percent.
- again, 43% of what?
- same "it" issue

The correct answer is C.