BEIJING (Reuters) - Sovereign debt troubles in Europe underscore how important it is for the United States to control its own borrowing as its indebtedness reaches concerning levels, a senior Chinese official said on Thursday. With China facing criticism for holding its currency in a de facto dollar peg, assistant finance minister Zhu Guangyao shifted attention to Beijing's own worries about U.S. policies, especially its soaring deficit, ahead of high-level bilateral meetings next week. There will be "quiet discussions" about the yuan at the Strategic and Economic Dialogue, but external pressure will only delay the exchange rate reform that China...