们要始终坚持和不断完善公有制为主体、多种所有制经济共同发展这一基本经济制度。这是

从H、C、O、N、Na、Fe、Ca、Cl、Na五种元素中选择适当的元素，填写符合下列要求的化学式：

①相对分子质量最小的氧化物______．②厨房用的酸性调味品______．

③铁锈的主要成分______．④能污染空气的一种气体______．

2007年8月《地球学报》杂志报道，利用氮、氧及氮、硼同位素技术，通过测定可知地下硝酸盐来源的水污染情况。完成下列填空：

（1）关于¹⁴N与¹⁵N的正确说法是           ；

a、自然界氮元素中¹⁴N的含量：空气中大于地壳中   b、单质：¹⁴N₂与¹⁵N₂互为同位素

c、电子层结构：¹⁴N与¹⁵N完全相同                d、原子半径：¹⁴N小于¹⁵N

与N元素同周期且最外层有2个未成对电子的元素相互组成的化合物属于           分子。（填：“极性”、“非极性”、“极性或非极性”）

（2）NH₃与H₂O分别能与H⁺ 结合成NH₄⁺与H₃O⁺。与NH₄⁺具有相同空间构型的微粒是             ；

a、H₃O⁺            b、CH₄          c、P₄            d、NH₃

分子中的键角：CH₄        P₄（填：“＞”、“=”或“< ”）。

（3）H₃O⁺ 与NH₄⁺ 的水溶液均显酸性。用离子方程式表示NH₄⁺ 水溶液显酸性的原因：

                                                    。

（4）使用N、O、 B同位素，并结合水化学分析，将更有利于对测定结果的解释。写出B原子的最外层电子排布式                 ；B原子核外的电子处在          个不同的能级上。

一个工作频率为400MHz的32位总线带宽为 【9】 MB／s。

开放性阅读。

     The power of nature Wind, water, fire and ice-these powerful natural forces shaped the land of America

in the past. They are still changing it today.

     The Colorado River slowly cut through stone to make the Grand Canyon.

     Long ago, ice sheets cut Yosemite Valley and glaciers (冰川) were moving in Alaska.

     Rains and storms hit the land from time to time. Fires sometimes burn down forests and destroy the homes

of wide animals. This happened in Yellowstone Park in 1998.

     Dead volcanic (火山的) mountains such as Haleakala on Moui and Crater Lake in Oregon are beautiful to

look at. There are also several active volcanoes in the US, especially along the Pacific Coast. There are also

many earthquakes in this area. Scientists can do nothing to control earthquakes or volcanoes. This was shown

clearly on May 18, 1980. At 8: 32 that morning, Mount St. Helens in Washington State erupted (爆发). The top

of the mountain was blown off.

     Over 60 people-campers, scientists, journalists, and forest workers were killed. Hundreds of square miles

of forests were knocked down. In towns over 100 miles away, day suddenly became night. An ash cloud hid

the sun for many hours. Town and fields in Washington, Oregon, and Idaho were covered with dirty grey ash.

     Scientists knew that Mount St. Helens could erupt soon but no one could say when. And no one expected

the terrible strength of the eruption. Many people were surprised and weren't ready. Harry R. Truman, 84,

owned a small hotel in Mount St. Helens. Scientists had asked him to leave because the volcano was becoming

dangerous.

     Harry Truman would not leave his home. Now it is covered with many feet of dirty ash. A small cross

stands above the place where Harry probably died. Perhaps it is better that he did not see what happened to

Mount St Helens, the once beautiful lake, and the forests.

     But slowly, life is returning to the dead area around the mountain. Grass and small plant are beginning to

grow again. Deer and birds have been seen in the area. The land will never be the same as it once was. Perhaps

Mount St. Helens will erupt again but this is all part of nature's pattern of change, and man has little power to

control it. 

根据短文内容，判断下列各句的正(T)误(F)。

( )1. The Colorado River slowly cut through stone to make the Grand Canyon.

( )2. Long ago, ice sheets made Yosemite Valley and the Great Lakes, and glaciers are not moving in Alaska.

( )3. Scientists knew exactly when Mount St. Helens would erupt.

( )4. Harry was finally persuaded to leave his home.

( )5. Now the land is not the same as it once was.

水份干燥用分子筛干燥的条件？