读下面“某国地势相似，地域相连的X、Y两地区之简况表”完成下题。

有X、Y、Z三种金属,把Y投入X(NO₃)₂溶液中,Y表面有X析出;把X投入Z(NO₃)₂溶液中,X表面有Z析出。X、Y、Z三种金属的活动性由强到弱的顺序是（   ）

（Ⅰ）用分层抽样的方法在35至50岁年龄段的教师中抽取一个容量为5的样本，将该样本看成一个总体，从中任取2人，求至少有l人的学历为研究生的概率；

（Ⅱ）在该校教师中按年龄状况用分层抽样的方法抽取N个人，其中35岁以下48人，50岁以上10人，再从这N个人中随机抽取l人，此人的年龄为50岁以上的概率为 $\frac{5}{39}$ ，求x、y的值．

   Good morning! Now let me report the discussion work in our group. Wu Jun cleans up rooms  ____  weekends and Jia Mei likes cooking dinner with her mum. Wang Ping sometimes  ____ (wash) clothes for her family. As for me, I usually help my father water the flowers.
   In my opinion, it is necessary  ____  us students to do some housework by doing it, we can help our parents and understand them better. We’ll also learn to take care of  ____ . Besides, we can relax ourselves from hard work and develop our abilities.
That’s all. Thanks for  ____  ( listen)!

如图是公共汽车上用电磁阀控制车门开、关的工作电路图．L₁、L₂是固定的电磁线圈．衔铁T_l、T₂通过横杆相连并可左右移动，带动传动装置使车门开启或关闭．S接通触点b时，线圈____ （填“L₁”或“L₂”）具有磁性，吸引衔铁使横杆向____ （填“左”或“右”）运动，带动传动装置关闭车门．