Explanation

Creating a filter: the original version of the sentence sounds poor, but so poor that it's probably easier just to go straight to the answer choices. The answer choices are diverse, so we can start with (B) and examine them one at a time.

Finding objective defects: choice (B) has a bad comparison between "similar size" and "California." We can't compare a size with a country, so (B) is out. In (C), the comparison is improved, but the phrase "but in Japan with" is redundant and awkward. Choice (D) sets apart the phrase starting with "but fully..." with a comma as if it's an independent clause, but it has no verb, so it is grammatically not viable. Choice (E) works: the comparison is correct, because "that" stands for "land area", and "of whom" refers to the population. Back to (A). Does (A) have an error? Yes; the word "where" does not actually refer to a place, as it must, but to a population. The correct answer is (E).