A:more than; who is
B:rather than; that are
C:other than; that is
D:less than; which are
已知扇形的周长为20,当扇形的圆心角为____ 弧度时,它有最大的面积.
如图是克隆羊多莉的培育过程,请回答:
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):