油画棒抗折力的标准要求是（） A.〉4N B.≥5N C.〉5N D.≥4N

岩体中的剪节理产状稳定，通常延伸很远，节理面上有擦痕，而且节理面多为（）。

A.粗糙不平 

B.平直、光滑 

C.锯齿状 

D.波状起伏

小明五次测试成绩如下:91、89、88、90、92，则这五次测试成绩的平均数是          ，方差是          

气焊使用的焊丝在焊接中的作用是（）。

A.保证焊缝的金属成分与组织

B.保护熔池金属不被氧化

C.填充金属

D.避免焊接产生气泡和裂纹

Jason had been watching the X Games on TV. Athletes from all over the world were competing in the most amazing sports. Just then his grandmother walked into the room. “I want to be extreme. Would you really let me do that? You always worry about my safety!” said Jason.

“You will have to follow some rules,” said his grandmother. “You can only ride in the park — never on the streets. You have to promise to wear a helmet (头盔). If you hurt yourself too much, I have the right to take your skateboard away. Is it a deal?”

“You bet!” Jason was so excited that he jumped off the sofa. A week later he had a board and a helmet.

On Saturday, his grandmother dropped him off near the park. He was happy to have a grandmother who let him try new things.

Kids in the park were moving quickly up and down the ramps (坡道). They flew into the air and landed as easily as birds. When he watched the X games, Jason felt like he was doing the tricks himself. But watching these kids up close, he knew that none of it was going to be easy. He felt a little bit scared.

Very slowly he carried his board to the ramp. Taking a deep breath, he put his right foot on the board. He kicked off with his left foot. For a few seconds he glided (滑行) along, just waiting to fall. Then he came to a stop. Kicking off again, he waited for the worst to happen. Again, he stayed up. The third time he kicked, lost his balance, and fell hard on his left knee.

It hurt, but it was no big deal! Why had he been so scared? Now he felt calm because things had gone wrong, and he was fine!

Next time he kicked off harder and went fast and farther. “Excellent!” said a girl as she passed him. “Extreme!” laughed Jason to himself. “Not quite.”

小题1:Jason’s grandmother agreed to let him try skateboarding unless _____.

A．he finished his homework

B．he liked the sport

C．he observed some rules

D．he won a bet小题2:Jason jumped off the sofa because _____.

A．he was allowed to go skateboarding

B．he was angry at his grandmother

C．he was going to play outside

D．he was given a board and a helmet小题3:The girl praised Jason for his _____.

A．skill

B．honesty

C．courage

D．kindness

柴油机（）的作用是连接活塞和曲轴，在膨胀作功过程中把气体力和往复惯性的合力传给曲轴，使活塞的往复运动转换成曲轴的旋转运动。

A、活塞组

B、连杆组

C、曲轴组

D、气缸组