Kaplan's Explanation -
Read the Original Sentence Carefully, Looking for Errors:
Note the verb "tells" in the underlined portion. Here the GMAT is testing a common error in a classic way, by assessing our ability to determine the correct subject-verb agreement by placing the subjects as far as possible from the verb to disguise the error. The singular "tells" does not agree with the plural subjects "direction and length." Always pay attention to verbs in underlined portions of GMAT Sentence Correction questions, and also pay attention to how the underlined portion ends, because that will likely be a source of variation among the answer choices.
Scan and Group the Answer Choices:
We know the first choice has incorrect subject-verb agreement, so we can throw out choice (A). Two other choices, (B) and (C), also have this incorrect subject-agreement, so we can eliminate them, too. Choices (D) and (E) both use a plural verb. One of them must be the correct answer.
Eliminate Choices Until Only One Remains:
We are left with choices (D) and (E). While choice (D) correctly uses "tell," the wording after the verb is awkward and confusing. The phrase "found to" is idiomatically incorrect. Only Choice (E) has the correct subject-verb agreement and is clearly written. Thus, Answer Choice (E) is correct.