藏在肤色背后的奇妙故事
People have different skin (皮肤) colors. Why? The sun is the answer.
Long long ago, people lived in places with strong sunlight. There, dark skin kept them safe from the sun. In places with less sun, the body needs sunlight to make vitamin D. Vitamin D helps keep our bones (骨头) strong. So over many, many years, people there came to have lighter skin.
Your skin can change a little, too. If you play outside a lot in summer, your skin may get darker. In winter, it gets lighter again.
Today, people travel to many different places. Whatever color your skin is, it has its own story. And staying safe in the sun is good for everyone.
1.1.Why is dark skin helpful in sunny places?
A It keeps people safe.
B It makes vitamin D.
C It makes bones strong.
D It keeps people warm.
解析：选A。A 细节理解题。根据第二段的“There, dark skin kept them safe from the sun.”可知，在阳光强烈的地方，深色皮肤能保护人们免受太阳伤害，也就是让人们更安全，所以选A。文中说的是阳光帮助身体制造维生素D，维生素D帮助骨骼强壮，因此B“制造维生素D”和C“使骨骼强壮”都不是深色皮肤的作用；D“让人保暖”文中没有提到，所以不选。
2.2.What does vitamin D do?
A It makes our skin lighter.
B It helps people travel far.
C It keeps us safe from the sun.
D It keeps our bones strong.
解析：选D。D 细节理解题。根据第二段“Vitamin D helps keep our bones strong”可知，维生素D有助于保持骨骼强壮，所以选D。A“让皮肤变浅”与文中意思不符，文中是说在阳光较少的地方，人们逐渐有了较浅的皮肤；B“帮助人们远行”文中没有提到；C“保护人们免受太阳伤害”是深色皮肤的作用，不是维生素D的作用，所以不选。
3.3. What may make your skin get darker?
A Reading books at home.
B Swimming in the sun.
C Staying in bed all day.
D Wearing a warm coat.
解析：选B。B 推理判断题。根据第三段“If you play outside a lot in summer, your skin may get darker.”可知，夏天经常在户外活动，皮肤可能会变黑。“在太阳下游泳”属于在户外阳光下活动，因此可能让皮肤变黑，所以选B。A“在家读书”、C“整天待在床上”、D“穿温暖的外套”都没有体现长时间在阳光下活动，不能使皮肤变黑，所以不选。
4.4. What is the passage mainly about?
A How to travel far.
B Summer and winter.
C Skin colors and sunlight.
D How to keep bones strong.
解析：选C。C 主旨大意题。文章先讲不同肤色与阳光有关，再讲阳光、维生素D和皮肤颜色变化，最后总结肤色都有自己的故事，并提醒在阳光下注意安全，因此全文主要围绕“肤色和阳光”展开，所以选C。A“如何远行”只在最后提到人们去不同地方，不是主旨；B“夏天和冬天”只是说明皮肤会变化的例子；D“如何保持骨骼强壮”只是维生素D作用的一个细节，不能概括全文，所以不选。