We all need to exercise. Doctors say it is good for us. It makes your heart and body strong. It also gives you more energy. And you will feel better yourself. It's best to exercise twice a week. Twenty minutes each time is enough.
   There are many ways to exercise. You can walk, run, play sports, or swim. Many people go to special places to exercise. They are called “fitness centers”. These places have a lot of equitment. Some people buy equitment for their homes. But it is very expensive.Exercising can be fun. Friends can exercise together at fithess center. Or they can play sports together, how do you exercise?

有人批评罗斯福新政的措施至今对美国仍有负面影响。下列措施最能体现“负面影响”的是

如图是甲、乙两物质（均不含结晶水）的溶解曲线，据此回答以下问题：

（1）t₁℃时，A物质的溶解度为____g；
（2）a点的含义是____；
（3）溶解度受温度影响小的物质是____；
（4）从A、B的混合物中分离A物质，一般采用____的方法．