We high school students do have some growing pains,____ we can get rid of them correctly and wisely. First, some of us are upset ____ their body styles and looks. It's unnecessary and it's not important at all. We needn't care about it. It is one's inner beauty____ matters. Second, we sometimes seem to be misunderstood by our teachers, parents and classmates.____ (face) with this, we can find ____ proper time to have a heart-to-heart talk with them, trying to remove the____(understand). Some of us have fewer in ends. I think being open-minded and friendly____ (do) you good. Third, we may fall behind others,____ makes us stressed. Actually we can encourage ____ to work efficiently, full of determination. Lastly, some of us don't have much pocket money, so they feel unhappy. Isn't it strange? So long as we have some, that's enough. And we can learn ____to spend money.

如图所示这四位同学描述的是同一化学符号，此化学符号是(  )

求证$\stackrel{-}{x}=\frac{x_1+x_2+\cdots {+}_n}{n},p={\left(x_1-\stackrel{-}{x}\right)}^2+{\left(x_2-\stackrel{-}{x}\right)}^2+\cdots +{\left(x_n-\stackrel{-}{x}\right)}^2$，q=（x₁﹣a）²+（x₂﹣a）²+…+（x_n﹣a）²若$a\ne \stackrel{-}{x}$则一定有（　　）