问题 选择题

下列物质的化学式和名称相符合的是(  )

A.氧化镁(OMg)

B.氧气(O)

C.氯化钙(CaCl)

D.硝酸银(AgNO3

答案

A、Mg元素的化合价为+2,O元素的化合价为-2,氧化镁的化学式应为MgO,所以A不正确;

B、氧气属于非金属气体,化学式应在元素符号下面加数字2,应为O2,所以B不正确;

C、Ca元素的化合价为+2,Cl元素的化合价为-1,两元素形成的化合物为CaCl2,所以C不正确;

D、Ag元素的化合价为+1,NO3的化合价为-1,形成的化学式为AgNO3,所以D正确.

故选D.

阅读理解

Today, over six billion people live on the planet. This means that there are very few places on Earth with no people. One place that has very few people is at the bottom of the Earth. In Antarctica, the icy continent surrounding the South Pole, you will not find anyone who lives there all the time.

First, Antarctica is the coldest place on Earth. For example, it can be –l30℃ in the winter. Humans cannot live in this kind of environment. Because it is so cold, very few plants or animals live there. This means there are no farms and no places to find wild plants or animals to eat.

Second, Antarctica can be dangerous. Many people think that it is safe to travel to Antarctica in the summer months when it is warmer. However, Antarctica is mostly ice, so when it’s summer, the ice melts. When the ice melts, the ice can break. So, people cannot travel around Antarctica during the summer. If the ice breaks, they could fall into the water and die.

Another serious problem in Antarctica is the sun. Because Antarctica is mostly ice, there are no trees so there is no shade. Also, the ground is mostly white ice so the sun bounces off (反射) it. The light from the sky and the light from the ground can burn people’s skin and hurt their eyes. People must be very careful in this situation. For example, they must wear sunglasses to protect their eyes. They must also cover their hands and faces all the time.

Although Antarctica is a tough place to live, explorers have discovered coal in Antarctica. This leads them to believe that Antarctica at one time was a land of swam (沼泽) and forests.

小题1:This text is mainly about _____.

A.the discovery of Antarctica

B.how people travel around Antarctica

C.different animals found in Antarctica

D.why it is difficult to live in Antarctica小题2:We can learn from the text that _____.

A.Antarctica is a place with no animals

B.no people can survive in Antarctica

C.Antarctica is colder than any other continent on Earth

D.the temperature in Antarctica is below zero all the time小题3:When is the most dangerous time to travel around Antarctica?

A.In spring.

B.In summer.

C.In autumn.

D.In winter.

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