The Australian dollar has fallen from 68.8 US cents on June 15 to 64 US cents this week. That's a drop of roughly 7 per cent — a significant drop for any currency, but especially the Australian dollar. The benchmark stock exchange index has also fallen 6 per cent from its all-time high. Every time a currency trader or a share investor buys or sells, there's a reason behind it — and the millions of decisions made every day by investors tell a story. The story forming now is one of worry. Concerns over the health of China's economy are...