This question presents a sentence, part of which or all of which is underlined. Beneath the sentence, you will find five ways of phrasing the underlined part. The first of these repeats the original; the other four are different. If you think the original is best, choose the first answer; otherwise, choose one of the others.
At least once each summer, skies darken and tornado sirens blare, and everyone hurries to take shelter in his basement.