一正电荷垂直射入匀强磁场中，其速度v的方向和受到的洛伦兹力F 的方向如图所示．下列关于磁场方向的说法中正确的是（   ）

     When I was about 13, I had an enemy, a girl who liked to point out my shortcomings (缺点). Sometimes she said I was lazy. Sometimes she said I wasn't a good student.____ . I tried to put up with (忍受) her as long as I could. At last, I became very angry. ____ .
    My father listened to me quietly, and then he asked, “Are the things she said true or not? Go and make a list of everything she said and mark the points that are true. Pay no attention to the other things she said.”
I returned to my room and I did as my father told me. To my surprise, I found that about half the things were true. ____ . He refused to take the list. “That's just for you,” he said. “When something said about you is true, you'll find it will be helpful to you. Listen to them all, but hear the truth and do what you think is right.”
     Many years have passed. ____. In our life we often meet with some trouble and we often go to someone and ask for advice. For some advice you will treasure (珍惜) all your life!

$\sqrt{4^2+3^2}$ ＝____，

$\sqrt{{44}^2+{33}^2}$ ＝____，

$\sqrt{{444}^2+{333}^2}$ ＝____，

$\sqrt{{4444}^2+{3333}^2}$ ＝____，

……

仔细观察上面几道题的结果，试猜想 $\sqrt{\underset{2011个}{\underbrace{44\cdots 4^2}}＋\underset{2011个}{\underbrace{33\cdots 3^2}}}$ ＝____.