先通读下面的短文，然后根据短文内容和所给首字母，在空格内填入一个适当的词，使短文意思完整。
    Mental health is about the way you think and feel and your ability to deal with ups and downs. Even though you are mentally healthy, it hardly m ____ that you don’t have a mental health problem.
    Mental health is everyone’s b____ . We all have times when we feel down or stressed. Most of the time those feelings pass, but sometimes they develop into a more serious problem. It seems that our mental health doesn't always s____  the same. It can change as the environment changes and as you move t ____ different stages(阶段) of your life.
    Here are four practical ways to look after your mental health. M ____  simple changes to how you live doesn't cost much or take up lots of time. Anyone can f ____ them.
●Talk about your feelings. It can help you stay in good mental health. It isn't a sign of weakness, but p ____ of your ability to do what you can to stay healthy.
●Eat well. What you eat and how you feel are c ____  connected. A proper diet can have a good effect on your mental health.
●Keep in touch. Friends and family members can offer various a ____  which may help you keep active and solve practical problems.
●Take a break. It could be a weekend exploring new places to enjoy the nature, or even a ten-minute break from doing your homework. A few minutes can be e____ to relax you.

阅读下列材料作答。

材料一：“上古之世，人民少而禽兽众，人民不胜禽兽虫蛇。”

材料二：“在北京人生活的洞穴里，用火遗迹十分集中。灰烬堆积很厚，最厚处有6米。”

材料三：“上古之世……民多疾病。有圣人作，钻燧取火以化腥臊，而民说之，使王天下，号之曰燧人氏。”

材料四：中华开国五千年，神州轩辕自古传。创造宫室、车船，平定蚩尤乱。世界文明，唯有我先。－－孙中山

1）.重庆位于我国西南，长江（Yangtze River）和嘉陵江（Jialing River）交汇处；

2）.推荐至少两个重庆的旅游景点（scenic spot）；

3）.邀请他到你家做客。

注意：

1）.词数100左右；

2）.可以适当增加细节，以使行文连贯；

3）.开头及结语已为你写好，不计入总词数。

Dear John,

    How is everything with you lately?

    Best wishes,

Li Hua

给出下列五个命题：
①某班级一共有52名学生，现将该班学生随机编号，用系统抽样的方法抽取一个容量为4的样本，已知7号、33号、46号同学在样本中，那么样本中另一位同学的编号为23；
②一组数据1,2,3,3,4,5的平均数、众数、中位数都相同；
③一组数据为a，0,1,2,3，若该组数据的平均值为1，则样本标准差为2；
④根据具有线性相关关系的两个变量的统计数据所得的回归直线方程为y=a+bx中，$b=2,\stackrel{-}{x}=1,\stackrel{-}{y}=3$则a=1；
⑤如图是根据抽样检测后得出的产品样本净重（单位：克）数据绘制的频率分布直方图，已知样本中产品净重小于100克的个数是36，则样本中净重大于或等于98克并且小于104克的产品的个数是90.

其中真命题为（    ）