China's central bank Chief and a trio of top government economists lined up on Friday to urge a cautious approach to economic reforms, defying increasingly urgent US demands for a swift revaluation of the currency.US Treasury Secretary John Snow told the Congress that he was confident that China would change the yuan’s decade-old peg of near 8.3 per dollar within the next six months.‘‘We’ve got their attention and they’re gonna move,’’” Snow told lawmakers, many of whom agree with US manufacturers that the peg unfairly undervalues the yuan by perhaps 30 per cent.But Zhang Yansheng of China’s powerful National Development and Reform Commission said a lot of work was still needed in areas such as currency, taxation and foreign trade policy in order to minimise the impact of yuan reform on China’s economy.China’s core problem was not whether the exchange rate of the yuan was too low, Zhang told the International Business Daily.