我国北方冬天比较寒冷，许多家庭安装了一种利用电来取暖的床﹣﹣“韩式电热坑”．其工作电路可简化为如图所示，其中K为保护开关，平常处于闭合状态，当温度超过某一警戒温度时自动断开，扇形导体S为旋转型选档开关，可绕0点旋转，每次都和相邻的两触点同时接触，从而实现关、低、中、高四个档位的转换（档位顺序未知，电功率越大档位越高）．小明在家里利用所学的物理知识来测量该电热炕的电功率．他先关闭家里其它所有的用电器，然后将S旋转到与触点1、2连接，观察发现家里标有“3000r/（kW•h）”的电能表的转盘在1min内刚好转了20转．已知R₁和R₂是发热电阻，R₂的阻值是R₁的2倍，其它电阻忽略不计，小明家电压恒为220V．完成下列问题：

选词填空

⑴Reading English ____  you to understand it. Many students never spend enough time (about 15 minutes) reading every day.   
⑵A ____ diet is very important for young students, so you can't eat too many hamburgers.
⑶Dad, what's the time? Is it time ____ now?
⑷The boy likes roller skating very much, but his father doesn’t have the time to take him to People's Square. So he often skates ____  his house.
⑸____  Miss Tian ____  Hunan or Sichuan? She eats so hot food.
⑹What is your uncle doing? He ____ his e-friends on the Internet.
⑺Sometimes she feels hungry ____ , so she eats an apple or a pear.
⑻Usually our parents____  new clothes____ us.
⑼What sports should I do to ____ ?  Swimming is the best sport.
⑽Cakes and sweets have____  sugar and are bad for your teeth.

笑笑的妈妈准备开一间专卖成年女鞋的鞋店，为此笑笑和小伙伴们想帮妈妈做个“进货”调查。   

庭中有奇树，绿叶发华滋。