如图是甲、乙两组同学分别设计的质量守恒定律的两个验证实验.请根据图示进行思考回答(假设甲、乙两组药品混合前质量均为m前、混合后质量均为m后):
如图,∠1+∠B=180°,∠2=45°,则∠D的度数是( )
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下列各图中,表示山脊的是( )