下列四个判断:
①某校高三一班和高三二班的人数分别是m,n,某次测试数学平均分分别是a,b,则这两个班的数学平均分为
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123834935197004/SYS201310251238349351970006_ST/0.png)
;
②10名工人某天生产同一零件,生产的件数是15,17,14,10,15,17,17,16,14,12,设其平均数为a,中位数为b,众数为c,则有c>a>b;
③从总体中抽取的样本(x
1,y
1),(x
2,y
2),…,(x
n,y
n),若记
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=
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123834935197004/SYS201310251238349351970006_ST/2.png)
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123834935197004/SYS201310251238349351970006_ST/3.png)
x
i,
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123834935197004/SYS201310251238349351970006_ST/4.png)
=
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123834935197004/SYS201310251238349351970006_ST/5.png)
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131025123834935197004/SYS201310251238349351970006_ST/6.png)
则回归直线y=bx+a必过点(
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);
④已知ξ服从正态分布N(0,σ
2),且p(-2≤ξ≤0)=0.3,则p(ξ>2)=0.2;
其中正确的个数有( )
A.0个
B.1个
C.2个
D.3个