题干

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
a
+
b
2
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(x1,y1),(x2,y2),…,(xn,yn),若记x-=
1
n
i=1nxiy-=
1
n
i=1nyi则回归直线y=bx+a必过点(x-,y-);
④已知ξ服从正态分布N(0,σ2),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

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B

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    You're growing up. That means you're probably experiencing changes, all at once. Your body is changing. It might even seem as if your entire self is changing. It can be confusing and even scary. ____ And it's good!

    Growing up means that you can do more, learn more, and start to make your mark on the world. In order for that to happen, your body produces chemicals called hormones that help both body and mind grow. Hormone levels change constantly, rising and falling.

    ____ But it's partly to blame for intense emotions, surprising reactions, and mood changes.

    Because of the way your brain develops, it is somewhat ruled by emotions now and through your teen years. As a result, growing up can seem like an emotional roller coaster (过山车)!____

    Take care of yourself. If you eat right, sleep enough, and get good exercise, your brain will be much more able to deal with the stress.

    ____ When you feel your moods changing or you're upset, or confused, some quiet time will allow you to gather your thoughts and get calmer.

    Practise relaxing your body and deep breathing when you go to bed.____ Plus, when stuff happens during the day, you'll be able to calm yourself quickly with a deep breath or two before you react. Your body is changing.

A. Take a timeout.

B. Work out regularly to keep physically fit.

C. But the truth is, it happens to every teen.

D. This changing is needed for your body's development.

E. It will help you fall asleep and start the morning right.

F. Here are a few things you can do to make the ride smoother.

G. Usually, these feelings settle down when you realize what is going on.