如图所示，两个皮带轮通过皮带传动（皮带与轮不发生相对滑动）．大轮半径是小轮半径的2倍，设A、B分别是大小轮轮缘上的一点，现比较它们的线速度v、角速度ω、周期T和频率f之间的关系，正确的是（   ）

①v_A：v_B=1：2         ②ω_A：ω_B=1：2

③T_A：T_B=1：2         ④f_A：f_B=1：2．

心情愉快是儿童青少年心理健康的核心．保持心情愉快的方法有以下三种：

方法一：____；方法二：____；方法三：____．

   We call the Chinese New Year the Spring Festival（春节）. There is a name for each Chinese year. We may call it the year of the sheep , the year of the monkey or the year of the dog. And this year is the year of the horse.
   Before New Year’s Day, people are busy shopping and cleaning their houses. On New Year’s Eve, there is a big family dinner. After dinner, all the family stay up late to welcome the New Year. On the first day of the New Year, people put on their new clothes and go to visit their friends and relatives（亲戚）. They say “good luck” and some other greetings to each other. People usually have a very good time during the festival.