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椭圆的焦点在y轴上,且,则这样的椭圆的个数为 .
设椭圆的焦点在y轴上,a∈{1,2,3,4,5},b∈{1,2,3,4,5,6,7},则这样的椭圆的个数是 ( )
(A)70 (B)35 (C)30 (D)20
(理)椭圆的焦点在y轴上,且m∈{1,2,3,4,5,5},n∈{1,2,3,4,5,6},则这样的椭圆的个数为________.