未知题型 差热分析与简单热分析有何不同？

单项选择题 初治肺结核患者应在治疗满2、5、6月时、复治肺结核患者在治疗满2、5、8月时均需复查痰涂片和培养，复查的肺结核患者应收集（）痰标本

未知题型 Use a graph to demonstrate the circumstances that would prevail in a competitive market where firms are earning economic profits. Can this scenario be maintained in the long run? Explain your answer.