两种液体的体积之比为3：5，质量之比为1：3，这两种液体的密度之比为(     )

下列实验方法操作，能达到要求的是（    ）

今年一季度，我市因治霾成效显著获得省治霾奖励。PM2.5是造成雾霾天气的元凶之一。下列行为不会增加大气中PM2.5的是（  ）

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”.

已知函数f（x）=sin² $\frac{\omega x}{2}$ + $\frac{1}{2}$ sinωx﹣ $\frac{1}{2}$ （ω＞0），x∈R，若f（x）在区间（π，2π）内没有零点，则ω的取值范围是（　　）