(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.
comparison should be between percent, and percent, not percent, and decade
(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.
comparison should be between percent, and percent, not percent, and decade
(C) Today, more than 43 percent of Californians under the age of eighteen are Hispanic, compared with about 35 percent a decade ago.
OK
(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.
Clearly wrong. It does not refer to anything, etc.
(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.
It does not refer to anything, etc.
Compare .. to and
Compare ... with, both are acceptable idioms.
When we try to equate A to B, you use 'A can be compared to B ...'.
When we try to see differeneces/similarities between A and B, you use 'A when compared with B is ....'.