Have you ever stayed in a hotel？Most Chinese hotels often provide guests with things like disposable（一次性的）toothbrushes，toothpaste，shampoo and slippers.Many guests like the idea because they don't have to bring their own.But，if you travel to Beijing，remember to bring your own things.Starting from June，some hotels in Beijing will no longer provide guests with these disposables.They want to ask people to use less disposable things.

Many disposable things are made of plastic.People throw them away after only using them once.It is a waste of natural resources（资源）and is very bad for the environment.Do you know，one Chinese person makes as much as 400kg of waste a year！Most of that waste comes from disposable things.In Beijing，people throw away about 19，000 tons of plastic bags and 1，320 tons of plastic lunch bowls every year！Plastic can take between 100 and 400 years to break down.So theless plastic we throw out，the better.So，wherever you travel，bring your own things and use them again and again.

Back at home and school，you can also do something to make our world a better place.Try to do these things in your daily life:Use cloth shopping bags，not plastic ones.After using a plastic bag，wash it out and let it dry.Then you can use it over and over again.Do not use paper cups.At your school canteen（食堂），use your own bowl and chopsticks instead of disposable ones.

Blue whales are the largest animals on the planet, and each year they undertake (进行) one of the longest migration (迁徙). After spending the summer in the Northeast Pacific, the whales travel thousands of miles to their breeding (繁殖) grounds off the coast of Central America.

To learn more about these behaviors, William Oestreich, a PhD candidate in biology at Stanford University, and his colleagues planted an underwater microphone, or hydrophone, just outside Monterey Bay and recorded whales’ songs over five years.

Only male blue whales are known to sing, but both sexes move southward at about the same time each year. Males and females have also been spotted pairing up and feeding together shortly before the migration begins. “That gives us some confidence that the sounds that are primarily being produced by males are fairly representative of what the whole population is doing,” Oestreich says.

During the summer, the songs picked up by the hydrophone took place mostly at night. The intensity of the songs reached the highest level each year between October and November. However, as winter approached and the songs dwindled, the whales changed to singing during the daytime. In the summer, blue whales spread out over vast distances while searching for food. By eavesdropping on (窃听) their distant neighbors at night, the whales may gather information about food conditions elsewhere in their range. Knowing when other whales are on the move could guide their decision about when to stop hunting for food and start their own journey toward milder waters.

By turning in too, we might be able to forecast when the whales will arrive in areas where they’re in particular danger of running into ships, such as the Santa Barbara Channel. “There have been quite a noticeable number of deadly collisions (碰撞) between ships and blue whales,” Oestreich says. “That could be one piece of the puzzle (拼图游戏) to more dynamically (动态地) managing those habitats and shipping paths in a way that allows shipping to continue, but also in a way that is safe for these whale populations.”

Our carbon footprint is the estimated amount of carbon dioxide given off as we go about our daily lives. While the global average carbon footprint is about 4 tons per person each year, Americans contribute approximately 20 tons of greenhouse gas per person each year. Compared to other countries, even those who use the least amount of energy in the US still contribute double the carbon emissions than the global average per person. And, not surprisingly, a person's carbon footprint increases in size as his or her income increases.

How is it possible that people in the US who live simple lifestyles, e.g., children or the homeless, make such large contributions to greenhouse gas emissions? The answer is simple: Each US citizen has access to various basic government services such as firefighting and police departments, road and bridge repair, libraries, prisons, the military, etc. When these public services are divided equally among the entire US population, it significantly raises the carbon footprint per person.

While it is admirable to make changes in lifestyle to reduce a carbon footprint, in reality, it is very difficult to do. The MIT study revealed that a "rebound effect" occurred when someone made an effort to reduce his carbon footprint. Take the example of a person who made the deliberate choice to buy a hybrid(混合动力的)car instead of a large SUV to save money on gas costs. Very often that person would use the money he saved to do something else, e.g., take a long airplane trip. In this case, just one long airplane trip produces more CO₂ emissions than driving the large SUV for a year. This ends up having a negative impact on a person's carbon footprint by making it bigger!

Can Americans reduce their carbon footprints? According to the study, it is possible, but it would require lifestyle changes such as giving up long distance travel and buying fewer smartphones and tablets that have large energy cost to produce and deliver. Another way is to add a CO₂ tax on food, housing, and transportation. Unless we can find a way to reduce our carbon footprints, the price we may ultimately have to pay is much higher than the amount Americans will ever have to pay in taxes.