在盛有氯化铜、氯化亚铁和氯化铁混合溶液的容器中加入铁粉和铜粉，讨论以下几种情况阳离子或金属单质存在：（用Cu、Fe、Fe²⁺、Cu²⁺、Fe³⁺等化学用语回答）

（1）反应后有铁剩余，则容器中固体还可能有____ ．

（2）反应后铜有剩余且有相当数量的Fe²⁺，则溶液中可能存在____ ．

（3）反应后溶液中有相当数量的Cu²⁺，则还可能有____ ．

（4）若反应后容器中除有相当数量的铜离子外，若还有相当数量的铜，则一定不存在的有____ ；若有相当数量的Fe³⁺存在，则一定不存在　____ ．

    Do you want to be happy? ____ They will help you become a happy person．

   ★Be thankful. There are so many things to be thankful for. ____ Thank your parents for preparing meals for you ; thank the school bus driver for driving you home safely and thank the mailman for bringing you your letters every day. By doing this you will feel happy．

   ★ ____ For example, read a good book , listen to your favorite music or spend time with your close friends. Don't spend too much time worrying about the future, such as going to college or getting a good job．

   ★ ____ You may forget about your trouble by joining in some activities like singing, dancing or swimming．★Help others. Many people feel happy after helping others ____ You can help a friend with his or her studies. You can read books for the children in your neighborhood. You can also be a volunteer to help the old or the disabled．

In the writer’s opinion, students can’t remember words because _______.

已知$\left\{\begin{array}{c}x=1\\ y=-1\end{array}\right.$是方程2x﹣ay=3的一组解，那么a的值为（　　）