题目

BEIJING—Apple Inc is one step closer to beginning sales of iPad2 tablet computers with cellular  network compatibility （兼容） for the first time in the Chinese mainland, where the consumer-electronics giant is in the midst of an aggressive expansion．        According to China’s Telecommunication Equipment Certification Center, a device by Apple with third-generation high-speed wireless data capabilities was issued the network access license needed for the company to begin official sales in China．The device, listed under model number “A1396”, is compatible with 已知，α－β是第一象限角，tanβ＝，β是第三象限角，则sinα的值为 [　　] A． B． C． D．