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You’ve probably heard “Don’t go outside in the winter with your hair wet or without a coat; you’ll catch a cold.” That’s not exactly true. As with many things, the reality is more complicated. Here’s the distinction: Being cold isn’t why you get a cold. But it is true that cold weather makes it easier to catch respiratory (呼吸的) viruses such as the cold and flu.

Virus transmission is easier when it’s cold. More specifically, cold weather can change the virus’s outer layer, making it tougher and more solid. Scientists believe that makes person-to-person transmission of the virus easier.

It’s not just cold winter air that causes a problem. Air that is dry in addition to cold has been linked to flu outbreaks. That’s because dry winter air further helps the virus to remain infectious longer. Dry air, which is common in the winter, causes the water found in respiratory droplets to evaporate (蒸发) more quickly. This results in smaller particles, which are capable of lasting longer and traveling farther after you cough or sneeze.

Also, most people get less sunlight in the winter. That is a problem because the sun is a major source of vitamin D, which is essential for immune system health. Physical activity, another factor, also tends to drop during the winter. People are three times more likely to delay exercise in snowy or icy conditions.

Instead, people spend more time indoors. That usually means more close contact with others, which leads to disease spread. Respiratory viruses generally spread within a 6-foot radius of an infected person.

Moreover, cold temperatures and low humidity can dry out your eyes and the mucous membranes (黏膜) in your nose and throat. This makes it easier for viruses like those causing colds, and flu to attach when you breathe them in.

What can you do? There are strategies to help prevent illness all year long.

1.1.Why do viruses remain infectious longer during winter?

A Dry air brings smaller particles.

B People cough longer in winter.

C More types of flu come in winter.

D Cold air weakens people’s immune system.

解析：选A。A 细节理解题。根据第三段最后两句可知，冬天干燥的空气会让呼吸道飞沫中的水分蒸发得更快，从而产生更小的颗粒，这些更小的颗粒能够持续更长的时间并传播得更远。故选A。

2.2.How could sunny days in winter affect one’s immune systems?

A The air is dryer and makes it easier for viruses to spread.

B People are more likely to catch a cold.

C People can get more vitamin D from the sunlight.

D People tend to stay indoors and exercise less.

解析：选C。C 细节理解题。根据第四段中的“That is a problem because the sun is a major source of vitamin D, which is essential for immune system health.”可知，维生素D的主要来源是皮肤在阳光照射下的自然合成，而维生素D对免疫系统至关重要。故选C。

3.3.The virus might spread faster when ________.①the virus’s outer layer becomes stronger ②we stand too close to an infected person③we spend most of the time at home ④we feel our nose and throat dry

A ①②③

B ①②④

C ②③④

D ①③④

解析：选B。B 细节理解题。根据第二段可知，寒冷的空气使病毒的外层更坚固，让病毒更容易在人与人之间传播，故①正确。根据倒数第三段可知，呼吸道病毒通常在感染者周围6英尺范围内传播，即站得离病毒源越近，越容易感染，故②正确。根据倒数第二段可知，低温低湿度会让鼻子和喉咙的黏膜变得干燥，在吸入病毒时就更容易附着，故④正确。故选B。

4.4.What will the text probably talk about next?

A The symptoms of common colds and flu.

B Approaches to prevent sickness throughout the year.

C The importance of vitamin D for immune health.

D The science behind virus transmission in cold weather.

解析：选B。B 推理判断题。根据最后一段的“There are strategies to help prevent illness all year long.”有一些策略可以全年帮助预防疾病，即接下来作者可能会介绍预防疾病的方法。故选B。