Have you ever heard someone use the phrase"once in a blue moon"？People use this expression to describe something that they do not do very often．For example，someone might say that he tries to avoid eating sweets because they are unhealthy，but will eat chocolate"once in a blue moon"．Or someone who does not usually like to go to the beach might say"I visit the shore once in a blue moon．"While many people use this phrase，not everyone knows the meaning behind it．

    The first thing to know is that the moon itself is never really blue．This is just an expression．In fact，the phrase"blue moon"has to do with the shape of the moon，not the color．

    As the moon travels around the earth，it appears to change shape．We connect names with certain shapes of the moon．For example，when we can see a small part of the moon，it is called a crescent moon．A crescent is a shape that looks like the tip of a fingernail（指甲尖）．When we cannot see the moon at all，it is called a new moon．When we can see the whole moon，it is called a full moon．Usually，there is only one full moon every month．Sometimes，however，there are two full moons in one month．When this happens，the second full moon is called"a blue moon"．

    Over the next 20years，there will only be 15blue moons．So you can seldom see a blue moon． This fact has led people to use the expression"once in a blue moon"to describe things they don't often do in their lives．

    Earlier this year, China achieved a new milestone(里程碑) in space exploration(探索). On Jan 3, Chang'e 4 became the first space probe(探测器) in history to land on the far side of the moon, People's Daily reported.
    From Earth, we can only see one side of the moon. The other side has been a mystery. Scientists have long wondered what lies on this side of the moon.

    Chang'e 4 has sent back photos of the far side of the moon. It is also used to carry out experiments, such as growing seeds in a low-gravity(低重力) environment. The data(数据) collected from these experiments could be used to help us build a base on the moon in the future.

    The success of the Chang'e 4 mission(任务) is a main achievement for China's space program. It marks a new stage in China's deep space exploration, said Wu Yanhua, head of China National Space Administration.

    China launched(启动) its lunar(月球的) exploration program in 2004, naming it Chang'e. Chinese scientists set three goals —“orbiting(环绕运行), landing and sample(样本) returning”— referring to launching probes that could circle around the moon, touch down on its surface and bring lunar materials back to Earth.

    Chang'e 4 has realized the goal of landing. The third will be achieved during the Chang'e 5 mission, which is set to take place before the end of this year, China Daily reported.

    Following the success of the Chang'e missions, Chinese scientists are looking even farther into our solar system (太阳系). China's first Mars(火星) mission is expected to be carried out by 2020, Wu said.

Tanzania (坦桑尼亚) is a country which has a lot of animals, such as gnus (角马), lions, cheetahs (猎豹), elephants, giraffes and crocodiles. Every year, many people in the world travel to this African country to watch the animals closely. But do you know how they travel?

By bus—This is the most common way. When people get on a bus, they'll find that the bus is a little strange. It is different from the buses we often see. There are no big windows at all, but some small windows. And it looks like a cage. What is it used for? Oh, people can use it to watch animals, especially those dangerous animals, and take photos.

By boat—We can often see that many people are on a boat, enjoying the beautiful sights along a river or a lake, and they can also enjoy hippos (河马) and crocodiles from a nearer distance.

By hot-air balloon—In the early morning, when the sun is beginning to rise, a large hot-air balloon is also starting its journey. Taking a hot-air balloon makes most of the travellers excited. After some time, the balloon will land in a certain place, and the waiters will serve people a delicious and special breakfast. But the cost of taking a hot-air balloon is also very high. A person should pay about 400 dollars for an hour's trip.

Plastic pollution is one of the most serious environmental problems all over the world. Many countries are looking for ways to solve the problem. On November 7，2022，China started a"Bamboo instead of Plastic" project with the International Bamboo Organization. It will hopefully reduce plastic pollution. 

Bamboo is a plant of great value，such as cleaning air and preventing soil going away. Unlike trees which usually need a long time to fully grow，bamboo can be put into use in 3 to 5 years. As long as it is protected well

China is one of the countries with plenty of bamboo in the world. The Chinese are a pioneer in the use of bamboo. Zhejiang Province has set up companies to produce and develop bamboo products. Many of them have been sold to over 100 countries. China is also sharing its technology to help India and Japan，the countries which are rich in bamboo. It is hoped that countries around the world will work together for global green development. 

Do you know "Lian Lian, Cong Cong, and Chen Chen"? They are the mascots (吉祥物) for the 19th Asian Games in Hangzhou. They are robots. "Lian Lian" stands for the West Lake. The West Lake is a world heritage site (世界文化遗产). Her name comes from the green leaves in the West Lake. It means clean and peace. "Cong Cong" stands for the world heritage site of Liangzhucity in Hangzhou. His name comes from the JadeCong. "Chen Chen" stands for the world heritage site of the Grand Canal. His name comes from the building of Gongchen Bridge on the Grand Canal.

After 16 days of exciting games, the 19th Asian Games in Hangzhou ended on October 8th. Many people think that "Lian Lian, Cong Cong, and Chen Chen" brought so much fun to China in 2023.

The design (设计) of the mascots "Cong Cong", "Lian Lian", "Chen Chen" come from a designer named Zhang Wen and his wife Yang Yihong. She is a young teacher.

A. The 3D Food Printer is a fantastic invention. It can"type out"all the food you wish to eat. When you want a dish, you just need to give the printer instructions and press the button. 

B. Samsung Sero is a smart TV. You can rotate(使旋转)the screen of the TV. It's more like a giant smartphone. It gives people the ability to watch Instagram stories and TikTok videos on a bigger screen. 

C. With Ember Cup, you can drink water at any time. By using a smart charging base(充电底座) and a special app, the cup can keep the water's temperature between 49℃ and 62℃. 

D. Norton Core is a special router(路由器). Different from other routers, Norton Core can be used to check your computer and smartphone. When finding something unsafe, it will quickly cut off the Internet to keep your computer and smartphone safe. 

E. Fresh air is important to us. Molekule is a smart purifier(净化器). It can take in something harmful in the air and kill germs and viruses in it with the help of the newest technology. 

F. E-Sight 3 is a kind of special glasses. They can help people with low vision(视力). A small, high-definition camera inside takes pictures of everything the user is looking at. And then the glasses turn these pictures into information that the user can"see".