设随机变量X和Y独立同分布，记U＝X－Y，V＝X＋Y，则随机变量U和V必然( )

单项选择题在市场经济体制中，价格不发挥以下哪个功能?( )

单项选择题The word 'covered' in paragraph 3, line 6, is closest in meaning toA.put onB.spread outC.extended overD.dealt with