When Wall Street awoke Monday to a massive sell-off in the Shanghai composite index, investors quickly trained a microscope on Apple shares, wondering how the company would fare if China's economy continued to slow. Even before the bell sounded, Apple shares dropped 5% in pre-market trading. After a day of sharp ups and downs,the stock closed down 2.5% at $103.12. Apple represents about 4% of the Dow's value. What became clear: As the world goes, so goes Apple — and the other way around.