下列各组物质中,互称为同位素的是: A.12C和14C B.氧气和臭氧 C.甲烷

题型:选择题

问题:

下列各组物质中,互称为同位素的是:

A.12C和14C

B.氧气和臭氧

C.甲烷和乙烷

D.正丁烷和异丁烷

考点:构成物质的粒子—分子、原子、离子元素周期律
题型:选择题

根据短文,补全文后的句子。

     There was a pilot (飞行员) and four people in a small plane. Suddenly there was something wrong

 with the machine while it was flying in the air.  The Smoke was everywhere in the plane.  The pilot told

 the people there were only four parachutes (降落伞).  They all became worried and started to make

  excuses.

    "I must go and mend the machine," said the pilot, taking one of the parachutes. There was nothing he

 could do so he jumped out.

    The first person stood up.   "I'm a doctor," he said. "I help people live longer and I save lives." He also

 took a parachute and jumped out.

    The next person said, "I must have a parachute.  I'm a very clever person.  I have to take part in an

 important sports match.  I know I'll win the game because I'll be the cleverest person there."  He picked

 up a pack and jumped out.

     Two men were left: an old businessman and a young mountain climber.  By this time the plane was

 going down fast. The businessman said, "Young man, I'm old but you're still young. You take the last

 parachute." The young mountain climber smiled. "Don't worry," he said. "We can both jump safely

 because there are still two parachutes.  Just now the clever person jumped out with my back pack

 (背包)."

1. All the people became worried because _____.

2. The "clever" man jumped out with _____.

3. All the People only thought of themselves except _____

4. From the story we know that ______ would be dead.

5. _____ was a kind-hearted man.

题型:选择题
估算.
78+69≈

345+689≈

851+249≈
976-452≈1374-299≈4519-502≈
题型:选择题

10%甲醛消毒液浸泡30分钟适用于( )

A.医用缝合线
B.刀片及剪刀
C.橡胶管
D.乳胶手套
E.输尿管导管

题型:选择题

人格障碍表现为()意志行为异常,感知和智力并无异常。

题型:选择题

跨境交付

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