设有一热机在环境温度为300 K时其热效率为20%，则该热机的高温热源的温度至少为(

某化学实验小组在实验室用加热大理石（CaCO₃）分解的方法制取生石灰（CaO）．加热一段时间后，同学们对大理石是否分解提出怀疑．小组同学经研究决定对加热容器内剩余固体的成分进行探究，以证明大理石是否分解．请你参与探究．

实验限选的试剂：稀盐酸、蒸馏水、二氧化碳．

提出问题：加热大理石（CaCO₃）后残留的固体成分是什么？

作出猜想：

猜想1：残留固体是CaCO₃

猜想2：残留固体是CaO

猜想3：残留固体是______．

设计实验，按要求完成下表：

Jonny Jones was a nice and popular boy, who everyone loved．He was so much fun, so good and so kind to everyone that they treated him wonderfully. But as everything he needed was given to him without asking, Jonny became a weed. He was so spoiled by everyone that he couldn’t stand any hardship.

One day Johnny heard a mother saying to her son “Come on, my boy, get up and stop crying. You are behaving like Johnny Jones.” That made Johnny feel very ashamed. But he was sure that he would prefer to be known as a good boy rather than a fool. Worried, he spoke to his father about all this, though he was afraid that maybe he would be laughed at for having such worries. His father, far from laughing at Johnny, told him that a teacher had taught him a secret trick to turn him into the toughest boy off all. “Eat a candy less, study a minute more, and count to five before crying.” Johnny asked, “Just that? ” “Yes, just that,” said his father, “It’s very simple, but I warn you that it won’t be easy.”

Johnny was happy like a bird, ready to follow the advice. He went to see his mother, and she noticed how happy he was when she offered him candies. “One candy less”, thought Johnny, so he only took one. That afternoon he had another chance to put it into practice by studying one minute more. The result was that he missed the first minute of his favorite program! But having achieved this gave him a great feeling of satisfaction. The same happened when he ran up against the corner of the kitchen table. He only managed to count to four before crying, but that was left deeply in his mother’s memory.

Over the following days Johnny kept using the motto in his life as his father told him. And the more he put this into practice ,the easier it got. Before long he realized that he could also do things that would seem impossible before.

小题1:The underlined word "weed" in the first paragraph refers to ____．

A．a person with a strong v/ill

B．a person with a weak character

C．a person who isn't popular with everyone

D．a person who changes his behavior according to the situation小题2:What made Jonny Jones decide to change himself?

A．A mother's words．              B．Others' attitude to him．

C．His father's advice．           C．His teacher's warning．

小题3:What is the key point of the advice from Jonny's father?

A．Eat fewer candies than before．

B．Count to five before crying．

C．Talk with parents and follow their advice．

D．Learn to control oneself and keep using the motto in life．小题4:What message does the writer want to convey through the story?

A．One should be brave to face his mistakes．

B．Nothing is difficult as long as you set your mind on it．

C．Spoilinga child too much may result in his selfish behaviors．

D．A strong will can be developed by small but consistent efforts．

"三偏征"的具体症状为（）

A.病变对侧偏瘫

B.病变同侧偏瘫

C.病变对侧偏身感觉障碍

D.病变同侧偏身感觉障碍

E.同向偏盲

允许速度υmax＞160㎞/h正线钢轨轨头总磨耗75kg/m超过（）判轻伤。

A、7mm

B、8mm

C、9mm

D、12mm

已知低碳钢、松木、混凝土抗压强度分别为415MPa、341MPa、29.4MPa，它们的表观密度分别为 7860kg/m³、500kg/m³、2400kg/m³，则它们的比强度之间的关系为( )。

A．钢材＞混凝土＞木材
B．钢材＞木材＞混凝土
C．木材＞钢材＞混凝土
D．混凝土＞钢材＞木材