People may find it unbelievable that two hundred years ago people did not link illness     1     environmental problems. In London, drinking polluted water led     2     many deaths from cholera. It always started in the poor neighborhood, and then it spread to the richer areas as the servants infected     3     the illness passed it on. Many doctors suspected    4    polluted water was     5     (blame). John Snow’s     6     (finding) proved that the dirtier the water, the     7     (severe) the illness. Therefore, they concluded that water must be     8     (pure). They instructed the     9     (handle) be removed from pumps if the water carried the virus. Thanks     10    John Snow, cholera was defeated eventually.

4 . Some scientists say that animals in the oceans are increasingly threatened by noise pollution caused by human beings.

The noise that affects sea creatures comes from a number of human activities. It is caused mainly by industrial underwater explosions, ocean drilling,and ship engines. Such noises are added to natural sounds. These sounds include the breaking of ice fields, underwater earthquakes, and sounds made by animals themselves.

Decibels(分贝) measured in water are different from those measured on land. A noise of one hundred and twenty decibels on land causes pain to human ears. In water, a decibel level of one hundred and ninety-five would have the same effect.

Some scientists have proposed setting a noise limit of one hundred and twenty decibels in oceans. They have observed that noises at that level can frighten and confuse whales.

A team of American and Canadian scientists discovered that louder noises can seriously injure some animals. The research team found that powerful underwater explosions were causing whales in the area to lose their hearing. This seriously affected the whales’ ability to exchange information and find their way. Some of the whales even died. The explosions had caused their ears to bleed and become infected.

Many researchers whose work depends on ocean sounds object to a limit of one hundred and twenty decibels. They say such a limit would mean an end to important industrial and scientific research.

Scientists do not know how much and what kinds of noises are harmful to ocean animals. However, many scientists suspect that noise is a greater danger than they believed. They want to prevent noises from harming creatures in the ocean.

7 . In the old days, when you had to drive to a movie theater or to a video store to get some entertainment, it was easy to see how your actions could have an impact on the environment. You were hopping into your car, driving across town, and using gas all the way.

But now that we’re used to staying at home and streaming movies, we might feel better about ourselves. After all, we’re just picking up our phones or maybe turning on the TV. You’re welcome, Mother Nature.

“Not so fast,” says a recent report from the French-based Shift Project. Watching a half-hour show would lead to 3.5 pounds of CO₂ emissions. That’s like driving 3.9 miles. According to “Climate Crisis: The Unsustainable Use of Online Video,” digital technologies are responsible for 4% of greenhouse gas emissions, and that energy use is increasing by 9% a year. Stored in data centers, videos are transferred to our terminals such as computers, smart phones, etc. via networks: all these processes require electricity whose production consumes resources and usually involves CO₂ emissions.

In the European Union, the Eureca project lead scientist, Rabih Bashroush, calculated that 5 billion downloads and streams of the song “Despacito” consumed as much electricity as the countries of Chad, Guinea-Bissau, Somalia, Sierra Leone and the Central African Republic used in a single year.

Streaming is only expected to increase as we become more attached to our devices. Online video use is expected to account for 80% of all internet traffic in five years according to CISCO. By then, about 60% of the world’s population will be online.

You’re probubly not going to give up your streaming services, but there are things you can do to help lessen the impact of your online use.

Here are some tips:

Disable autoplay for video on social media.

Stream over Wi-Fi, not mobile networks.

Watch on the smallest screen you can.

Don’t use high-definition (高清) video on devices.