在下图中，∠1=∠2，能判断AB∥CD的是（   ）

如图所示的装置中，A、B是两个架在绝缘支座上的金属球，原来都不带电，中间用导线连接．现用一个带正电的小球C靠近B球，用手摸一下B球，然后撤去导线，再拿走小球C，那么（　　）

为缓解昆明城市交通拥堵状况，下列措施无效的是（   ）

式子$\sigma \left(a,b,c\right)$满足$\sigma \left(a,b,c\right)=\sigma \left(b,c,a\right)=\sigma \left(c,a,b\right)$，则称$\sigma \left(a,b,c\right)$为轮换对称式．给出如下三个式子：①$\sigma \left(a,b,c\right)$=abc； ②$\sigma \left(a,b,c\right)=a^2-b^2+c^2$；③$\sigma \left(A,B,C\right)=\cos C·\cos \left(A-B\right)-{\cos }^{2}C$（A,B,C是$△ABC$的内角）．
其中，为轮换对称式的个数是（       ）

先通读下面的短文，掌握其大意，然后在每小题所给的A、B、C、D四个选项中，选出可以填入空白处的最佳选项。
    Some young people are worrying about acnes(青春痘) on their faces, and some are worrying about their figures(身材). Do you know 1 on earth（到底，究竟） the secret of beauty is? Think of smile and health, and then you may find the 2 .
    Maybe you are not 3 with your big nose, your small 4 or your weight(体重). Don't waste energy and feelings on the way you look . In fact, when you become an 5 and look at pictures of your past time, you'll find how cute you are.
    6 is the best way to make you beautiful. When people are happy, they look nice. When people smile or laugh from the7 of their hearts(心脏), they look very beautiful.
    Don't worry about your weight too much. Don't 8 food for it. No one lives 9 health. So you need to eat healthy food and do enough exercise.
    When you accept（接受） what you have 10 and enjoy them, you will really become pretty “inside and out”.