A、About 20 years. B、About 30 years. C、About 50 years. D、About 40 years. B文中第四段最后一句提到了全球限制存在了超过30年，可以得出答案，在阐述时间时，句子采用补充说明的形式，故可以

Since last December, China was preparing to open U.S. market on clothing and textile. China’s exports of cloth lng and textile products to the United States jumped more than 50 percent in the first eight months of 2005 to nearly $17.7 billion following the end of a global quota system on January 1.
    That prompted U.S. textile producers to seek protection under a "safeguard" provision of China’s 2001 entry into the World Trade Organisation since April. The measure allows WTO members to restrict the growth in imports from China to 7.5 percent annually when there is a market-disrupting rush.
    The Bush administration has imposed safeguard restricts on billions of dollars’ worth of Chinese clothing imports this year. But because the restricts have to be renewed annually ,textile groups have pushed for a comprehensive agreement that would limit imports until 2008 when the safeguard provision ends.
    US textile and clothing companies and their labor unions were pushing for a comprehensive deal to prevent a flood of Chinese imports that began last January when global quotas, in place for more than three decades, were lifted.
    Cass Johnson, president of the National Council of Textile Organizations, said on Sunday the new textile agreement was expected to restrict 34 categories of clothing and textile imports from China through 2008.