Explanation

Creating a filter: in this question, we might get tripped up in reading the original sentence right around the comma after "distance." The phrase starting with "designed" sounds as if it is modifying "distance," counter to the intended meaning. We can probably find an answer choice that expresses the intended meaning more clearly.

Applying the filter: Choices (D) and (E) dispel the problem. Choice (D) puts "both" in the wrong place and (E) has it in the right place. It's only designed once but for two purposes, so "both" should be right after "designed." In fact, (E) is the only answer choice that has that detail correct. The correct answer is (E).