Why do some birds vary from place to place in their song repertoires of according to DK?
A.
It comes about perhaps because of the change of their DNA.
B.
It comes about simply due to imitation of the other birds' manner.
C.
Because the birds have learned the local dialect by learning the loca} dialect from generation to generation.
D.
Both A and C
拍照语音搜题,微信中搜索"皮皮学"使用
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知识点:
皮皮学刷刷变学霸
举一反三
【简答题】设a∈[-2,0],已知函数 f(x)= x 3 -(a+5)x, x≤0 x 3 - a+3 2 x 2 +ax, x>0 (Ⅰ) 证明f(x)在区间(-1,1)内单调递减,在区间(1,+∞)内单调递增; (Ⅱ) 设曲线y=f(x)在点P i (x i ,f(x i ))(i=1,2,3)处的切线相互平行,且x 1 x 2 x 3 ≠0,证明 x 1 + x 2 + x 3 > 1 3 .