Which of the following is a sentence fragment?

AThe chain of events unfolded this way: Clara and Melvin went fishing, their boat engine broke down, and a storm rolled in.

BThe slogan—"Everyone needs one"—for the product.

CHigh above the city a balloon floated it drifted for hours on end.

DThe writer furrowed his brow, glared at the paper, and, eventually, wrote.