阅读理解 Spring, summer, autumn, and winter

题目：

阅读理解

     Spring, summer, autumn, and winter bring changes in the weather, plant and animal life, and the length

of days and night. Seasonal changes such as these are due to three factors, the tilt (倾斜) of Earth's axis (轴) to one side; the rotation, or turn, of Earth on its axis every 24 hours; and the revolution of Earth

around the sun once every year. Since Earth remains titled in the same direction during its revolution of

the sun, our distance from the sun changes, causing us to experience the changing seasons.

     In summer the Northern Hemisphere (半球), where we live, points toward the sun, bringing us closer

to it and its more direct and powerful rays. Six months later, when Earth is halfway through its revolution

around the sun, the Northern Hemisphere is tilted away from the sun, placing us farther from it and

exposing us to the weak rays of winter. The seasons in one hemisphere are opposite those in the other

hemisphere. However, one area of the Earth - the equator (赤道) - is always closest to the sun, so

equatorial regions experience hot weather throughout the year. In contrast, the polar regions, always

farthest from the sun, experience continuous frigid weather.

     In the Northern Hemisphere, we observe a gradual alteration in the angle of the sun during the year.

About June 21, on the summer solstice, or the first day of summer, the midday sun reaches its highest

point in the sky and produces the year's maximum daylight hours. About September 22, on the autumn

equinox, the midday sun is lower in the sky. Because Earth's axis is titled neither toward nor away from

the sun, equal periods of daylight and darkness result. About December 21, on the winter solstice, or the

first day of winter, the midday sun is at its lowest point in the sky. This brings the year's fewest daylight

hours. About March 21, on the vernal equinox, or the first day of spring, the midday sun is higher in the

sky. Daytime and nighttime hours are again equal.

1. This passage is mainly concerned with ____________.

A. how Earth rotates on its axis

B. why the various seasons occur

C. why each season is three months long

D. which parts of Earth are coldest

2. What happens on the summer solstice? 

A. The midday sun reaches its lowest point in the sky.

B. Earth's axis is tilted neither toward nor away from the sun.

C. There are equal periods of daylight and darkness.

D. The midday sun produces the greatest number of daylight hours during the year.

3. In the last paragraph, the writer presents facts about equinoxes and solstices to explain _________.

  A. why it is hot at the equator

  B. the various lengths of day and night

  C. why the midday sun is directly overhead

  D. the date of the autumn equinox

4. In this passage, the underlined word "revolution" in the first paragraph means ____________.

A. a great change

B. an uprising

C. standing still

D. circling