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问题 填空题

请用化学用语填空：

（1）地壳中含量最多的金属元素______； （2）2个镁离子______；

（3）天然气的主要成分______； （4）高锰酸钾中锰元素显+7价______．

答案

（1）含量最多的元素有氧、硅、铝、铁、钙，所以最多的金属元素是铝；

（2）离子的表示方法：在表示该离子的元素符号右上角，标出该离子所带的正负电荷数，数字在前，正负符号在后，带1个电荷时，1要省略．镁离子带2个单元位的正电荷，所以答案为2Mg2+；

（3）天然气的主要成分是甲烷，要记住其化学式的写法；

（5）元素化合价的表示方法：确定出化合物中所要标出的元素的化合价，然后在其化学式该元素的上方用正负号和数字表示，正负号在前，数字在后，所以答案为：K

+7
Mn
O4．

所以本题答案为：（1）Al；（2）2Mg2+；（3）5CO32-；（4）CH4；（5）K

+7
Mn
O4．

多项选择题

社会工作者小芳开展了一个军休老人康乐小组。在开展第一次小组活动时，小芳的工作重点应有（）。

A.营造信任的小组气氛

B.厘清组员的期望

C.解决组员间的价值冲突

D.制定小组规范

E.促进组员间的良性竞争
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单项选择题

Lichens may grow on the bark of a tree in a steaming tropical rain forest, on the bricks of big city buildings, on rocks in hot springs, on wind-swept mountaintops, and in the driest desserts. In the arctic, they provide the principal food for caribou, and they are one of the few plants that grow in Antarctica. They are pioneers, appearing in barren rocky areas and starting the formation of soil in which mosses, then ferns, and then other plants can take root.
Lichens are a partnership of two plants — fungi and algae. The lichen body is made up of a network of fungal strands. In the upper layers of these grow groups of algae. The two organisms live together to the benefit of both, a relationship known as symbiosis. The fungi provide support, absorb water, and shelter the tender algae from direct sunlight. The algae carry on photosynthesis and provide the fungi with food. The algae can live independently and are recognizable as a species that grows alone. The fungi, on the other hand, cannot live apart from their partners. They can be placed in known classes of fungi but are unlike any species that lives independently.
So definite are the form, color, and characteristics of these double organisms that for hundreds of years, they were classified as one. More than 15,000 "species" were named. If these organisms are classified as separate species, it is difficult to fit them into the existing system of classification. But if they are classified separately, these species of fungi seem rather strange. Lichens are a splendid example of the difficulties faced by taxonomists in classifying species.

Why does the author call lichens pioneers

A．Because they developed so early in the history of the planet.
B．Because of their primitive structure.
C．Because they prepare soil for other plants.
D．Because they were the first plants to live in Antarctica .
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