单选题 .  ①Historian Colin Calloway argues that in the late colonial period preceding the American Revolution (1775-1783), the British government sought to seal off territory west of the Appalachian Mountain from the encroachment of land-hungry White settlers, to negotiate with Native American peoples as independent foreign states, and to guarantee the integrity of traditional native American hunting grounds. ②By contrast, White Americans, released by the out break of the Revolution from the constraints of Britain's allegedly benevolent policies, are portrayed by Calloway as ruthless land-grabbers whose new national government endorsed their rapacity. ③Bernard Bailyn argues, however, that the "Americans" who encroached on Native American land during the Revolution had been British only a few years before. ④When, during and after the Revolution, White Americans seized Native American land by any available means, they were continuing a tradition dating back to the earliest years of English settlement in North America. ⑤And, according to Bailyn, the British government's prewar efforts to preserve the trans-Appalachian west for Native Americans resulted not from humanitarian virtue or ethnic tolerance but from British Merchants' desire to maintain their lucrative trade with native Americans and the government's desire to control immigration and avoid costly conflict between White and Native Americans over land.38.  The primary purpose of the passage is to ______