HONG KONG (AP) — Trading began Monday on a new cross-border stock trading link between Hong Kong and the neighboring Chinese city of Shenzhen, the latest step to widen access to China's markets for global investors. Hong Kong's top leader and the stock exchange's chairman marked the occasion by banging a gong in a ceremony connected by live videolink to their counterparts in Shenzhen, where officials rang a bell to kick off trading. Unlike Shanghai, a center for many lumbering, state-owned enterprises, Shenzhen's market is dominated by small, fast-growing private companies in up-and-coming sectors such as technology and health-care.