乙烷的分子式是（）。A、C2H6B、C4H8C、C6H10D、CH4

如何理解《素问•六节藏象论》中“肾者，主蛰，封藏之本，精之处也”？

患者，女，13岁，上下牙拥挤Ⅲ°，安氏Ⅱ类上颌前突，骨性高角患者，ANB8°，下颌向前方的生长发育已相当有限。

对此患者应采取的矫治计划为（）

A.拔除和

B.拔除和

C.拔除

D.拔除

E.拔除和

阅读理解。

      One morning I was woken by my mother's angry voice. I opened my eyes and found it was seven forty,

so I jumped out of bed and rushed to a nearby bus stop without breakfast. Fortunately the bus started going

as soon as I got on it. I was sure I could reach the school before the bell rang.

      However, the bus suddenly stopped. There was something wrong with it and we had to get off and wait

for another one. I felt I couldn't wait and the school was only fifteen minutes' walk, so I ran to the school as

fast as possible. Just at this moment, it began to rain hard.

      I reached the classroom with all my clothes wet through. Mr. Smith, our physics teacher, had begun his

class. I was always afraid of him. I hesitated (犹豫) for a moment, and then I opened the door.

      "It's you again, Jim," Mr. Smith said angrily. "I've told you not to be late, but you …". Then he suddenly

stopped when he noticed my wet clothes. He quickly took off his own jacket and asked me to put it on. "I

don't want you to catch a cold," he said kindly. I went to my seat with Mr. Smith's jacket on. It was a bit

large for me but I felt very warm in it. I found, for the first time, Mr. Smith's physics class so interesting and

I changed my mind, there and then, about being afraid of him.

1. According to this passage, classes in Jim's school probably began at _____.[ ]

A. 9 am

B. 8 am

C. 7 am

D. 7:30 am

2. Why did Jim hesitate before he opened the door? [ ]

A. He was afraid of facing Mr. Smith.

B. He didn't like to have the physics class.

C. Mr. Smith didn't let him go into the classroom.

D. He didn't want to interrupt others.

3. Jim found Mr. Smith physics lesson interesting that day because _____. [ ]

A. he knew physics was very important

B. he wanted to go to famous university

C. he didn't want to fall behind the others

D. he was moved by his physics teacher

4. We can infer from the passage that _____. [ ]

A. Jim usually went to school by bike

B. it was the first time Jim had been late

C. Jim was often late for school

D. Jim's mother also got up late that morning

强化零件表面是为了在零件表面形成（）状态，以提高零件表面的疲劳强度。

A．压应力

B．拉应力

C．交变应力

D．切应力

简述沿轨道运动的动画。