The word "day" has two meanings. When we talk about the number of days in a year, we are using
"day" to mean 24 hours. But when we talk about day and night, we are using "day" to mean the time
between sunrise and sunset. Since the earth looks like a ball, the sun can shine on only half of it at a time.
Always one half of the earth is having day and the other half night. A place is moved from day into night
and from night into day over and over by the spinning (旋转)of the earth. At the equator (赤道) day and
night are sometimes the same length. They are each twelve hours long. The sun rises at 6 o'clock in the
morning and sets at 6 o'clock in the evening. For six months the North Pole is tilted (倾斜) toward the sun.
In those months the Northern Hemisphere (半球) gets more hours of sunlight than the Southern
Hemisphere. Days are longer than nights. South of the equator nights are longer than days. For the other
six months the North Pole is tilted away from the sun. Then the Southern Hemisphere gets more sunlight.
Days are longer than nights. North of the equator nights are longer than days. Winter is the season of long
nights. Summer is the season of long days.

1. A place is moved from day into night and from night into day over and over by _____ of the earth.

A. the pushing
B. the pulling
C. the spinning
D. the passing

2. At the equator day is as long as night _____.

3. When the North Pole is tilted toward the sun, the Northern Hemisphere gets _____ sunlight.

A. less
B. more
C. all
D. no

     When you run downhill, gravity pulls you. When you throw a ball up, gravity pulls it down. When you
sit, gravity holds you down. When you lie down, gravity holds you to the bed.
     We know gravity is everywhere even though we can't see it.We know it pulls on every stone and every
drop of water. It pulls on everything.
     The gravity of the earth pulls everything towards the center of the earth.You know this when you try to
lift a heavy stone. Gravity pulls it down. The more the stone weights, the more gravity pulls on it. To lift
the stone, you must pull up harder than gravity pulls down. 
    The earth has gravity and the moon also has gravity. The moon has less gravity than the earth has. This
means the moon's gravity does not pull as hard as the earth's gravity.
     Do you weigh 60 kilograms? That means the pull of the earth's gravity on you is 60 kilograms. If you
were on the moon, you would weigh only 10 kilograms. The pull of the moon's gravity on you would be
only 10 kilograms.

1. The word "gravity" in the passage means "______" in Chinese.

A. 物体质量
B. 物体重量
C. 万有引力
D. 宇宙能量