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【单选题】
关于x,y的方程x 2 +m y 2 =1,给出下列命题: 1当m<0时,方程表示双曲线; 2当m=0时,方程表示抛物线; 3当0 <1时,方程表示椭圆。4当m=1时,方程表示等轴双曲线;5当m>1时,方程表示椭圆。其中,真命题的个数是( )
A.
2
B.
3
C.
4
D.
5
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