Question

    Have you ever spent an afternoon in the backyard, maybe grilling or enjoying a basketball game, when suddenly you notice that everything goes quiet? There is an old phrase “calm before the storm”, often used in a situation---a quiet period just before a great activity or excitement. According to our own experience, we know there is actually calm before the storm. But what causes this calm? And is it always calm before the storm?

A period of calm happens in a particular kind of storm, the simplest kind of storm---a single-cell thunderstorm. In this type of thunderstorm, there is usually only one main stream of current, which is warm, damp air and drawn from places near the ground. Storms need warm and damp air as fuel, so they typically draw that air in from surrounding environment. Storms can draw in the air that fit their need from all directions—even from the direction in which the storm is traveling.

As the warm, damp air is pulled into a storm system, it leaves a low-pressure vacuum(真空) coming after. The rising air meets the cold dry air that has already existed in the storm clouds, thus the temperature of the warm, damp air drops, and the water vapor in it changes into tiny drops that are a precondition of rain. These drops accumulate and build on larger particles(颗粒) like dust, until they grow large enough to form raindrops.

This warm, damp air keeps moving upwards, but it becomes cooler and drier during its trip through cloud. When it reaches the top of the cloud, the air is squeezed out at the top. This air is sent rolling out over the big thunderclouds. From there, the air goes down. Warm and dry air is relatively stable, and once it covers a region, that air, in turn, causes the calm before a storm.

Most thunderstorms, though, don't start with calm. That's because most are actually groups of storms with complex wind patterns. There's so much air moving up and down storm groups that the calm before the storm never happens. Instead, before the storm, it might be really windy!

1.Which best fits the description of a particular kind of storm?

A. A thunderstorm with a single shape.

B. A thunderstorm without strong winds.

C. A storm with air drawn from every direction.

D. A storm fueled by moving air from the ground.

2.What does the underlined word “it” in Paragraph 3 refer to?

A. Warm and wet air. B. Warm and dry air.

C. Cold and wet air. D. Cold and dry air.

3.Which does the writer most likely agree to?

A. Presence of the calm relies on stable air.

B. All thunderstorms don’t start with the calm.

C. The drier the air is, the bigger the storm will be.

D. Storm happens without air moving up and down.

4.What is the passage mainly about?

A. A brief introduction of a peaceful storm.

B. A personal experience of a heavy storm.

C. An explanation of the calm before a storm.

D. An analysis of causes and effects of a storm.

Answer

1.D

2.A

3.B

4.C

【解析】

本文是一篇说明文，解释了暴风雨来临前的平静的原因，并指出并非所有的暴风雨都始于平静。

1.细节理解题。根据第二段中的“In this type of thunderstorm, there is usually only one main stream of current, which is warm, damp air and drawn from places near the ground.”可知，在这种类型的雷暴中，通常只有一股主要气流，那就是来自地面附近温暖潮湿的空气，由此可知，特殊的雷暴是指由地面移动的空气推动的风暴，故D项正确。

2.词义猜测题。根据画线词前的“The rising air meets the cold dry air that has already existed in the storm clouds, thus the temperature of the warm, damp air drops”可知，上升的空气与干冷空气相遇，因此温暖潮湿的空气的温度下降，其中的水蒸气变成微小的水滴，这是下雨的先决条件，由此可知画线词指的是前面提到的温暖潮湿的空气，故A项正确。

3.推理判断题。根据最后一段中的“Most thunderstorms, though, don't start with calm.”可知，然而，大多数雷暴并非始于平静，由此可知，并非所有的暴风雨都始于平静，故B项正确。

4.主旨大意题。根据第一段中的“But what causes this calm? And is it always calm before the storm?”可知，本文主要解释了暴风雨来临前的平静的原因，故C项正确。