Astronauts on shorter shuttle missions（使命）often work very long days. Tasks are scheduled so tightly that break times are often used to finish the day's work.  This type of schedule is far too demanding for long missions on the International  Space Station（ISS）.  ISS crewmembers usually live in space for at least a quarter of a year. They work five days on and two days off to mimic the normal way they do things on Earth as much as possible . Weekends give the crew valuable.  Weekends give the crew valuable time to rest and do a few hours of  housework.  They can communicate with family and friends by email , internet phone and through Private video conferences.

    While astronauts cannot go to a baseball game or a movie in orbit, there are many familiar activities that they can still enjoy . Before a mission. The family and friends of each ISS crewmember put together a collection of family photos, messages, videos and reading material for

    The astronauts to look at when they will be floating 370 kilometers above the Earth.  During their mission, the crew also receives care packages with CDs, books, magazines, photos and letters . And as from early 2010, the internet became available on the ISS , giving astronauts the chance to do some “web surfing （冲浪）”in  their personal time.  Besides relaxing with these more common entertainments, astronauts can simply enjoy the experience of living in space.

    Many astronauts say that one of the most relaxing things to do in space is to look out the window and stare at the universe and the Earth's vast land mass and oceans.

China is a land of bicycles. At least it was back in 1992 when I traveled the country. Back then everyone seemed to be riding a bicycle. Millions of them，all black. Cars were rare. Yet since my arrival in Beijing last year，I've found the opposite is true. There are millions of cars. However，people still use their bicycles to get around. For many，it's the easiest and cheapest way to travel today. Bicycles also come in different colors—silver，green，red，blue，yellow，whatever you want.

    It's fun watching people biking. They rush quickly through crossroads，move skillfully through traffic，and ride even on sidewalks（人行道）.Bicycles allow people the freedom to move about that cars just can't provide.

    Eager to be part of this aspect of Chinese culture，I decided to buy a bicycle. Great weather accompanied my great buy. I immediately jumped up on my bicycle seat and started home.

    My first ride home was orderly（守秩序的）．To be safe，I stayed with a “pack”of bikers while cars on the streets came running swiftly out of nowhere at times.I didn't want to get hit. So I took the ride carefully.

    Crossing the streets was the biggest problem. It was a lot like crossing a major highway back in the United States. The streets here were wide，so crossing took time，skill and a little bit of luck.

    I finally made it home. The feeling on the bicycle was amazing. The air hitting my face and going through my hair was wonderful. I was sitting on top of the world as I passed by places and people. Biking made me feel alive.

    Since English biologist Charles Darwin published On the Origin of Species in 1859, scientists have vastly improved their knowledge of natural history. However, a lot of information is still of the speculation, and scientists can still only make educated guesses at certain things.

    One subject that they guess about is why some 400 million years ago, animals in the sea developed limbs (肢) that allowed them to move onto and live on land.

    Recently, an idea that occurred to the US paleontologist (古生物学家) Alfred Romer a century ago became a hot topic once again.

    Homer thought that tidal (潮汐的) pools might have led to fish gaining limbs. Sea animals would have been forced into these pools by strong tides. Then, they would have been made either to adapt to their new environment close to land or die. The fittest among them grew to accomplish the transition (过渡) from sea to land.

    Romer called these earliest four-footed animals “tetrapods”. Science has always thought that this was a credible theory, but only recently has there been strong enough evidence to support it.

    Hannah Byrne is an oceanographer (海洋学家) at Uppsala University in Sweden. She announced at the 2018 Ocean Sciences Meeting in Oregon, US, that by using computer software, her team had managed to link Homer's theory to places where fossil deposits (沉积物) of the earliest tetrapods were found.

    According to the magazine Science, in 2014, Steven Balbus, a scientist at the University of Oxford in the UK, calculated that 400 million years ago, when the move from land to sea was achieved, tides were stronger than they are today. This is because the planet was 10 percent closer to the moon than it is now.

    The creatures stranded in the pools would have been under the pressure of “survival of the fittest”, explained Mattias Green, an ocean scientist at the UK's University of Bangor. As he told Science, “After a few days in these pools, you become food or you run out of food... the fish that had large limbs had an advantage because they could flip (翻转) themselves back in the water.”

    As is often the case, however, there are others who find the theory less convincing. Cambridge University's paleontologist Jennifer Clark, speaking to Nature magazine, seemed unconvinced. “It's only one of many ideas for the origin of land-based tetrapods, any or all of which may have been a part of the answer,” she said.

    Sydney has a huge bus system(系统). No buses accept cash, and a ticket needs to be bought ahead of time. The buses often run at busy hours and regularly(有规律地) during the day. The Sydney Explorer bus provides air-conditioned service and stops at 27 tourist attractions. Its partner, the Bondi Explorer, stops at 19 attractions. Tickets allow holders to jump on and off as they please, and they are valid(有效的) for one or two days. It's an easy way to see the city and the surroundings.

    Sydney's train service runs throughout the central city area and the surroundings. Tickets can be bought from machines that operate 24 hours a day or from ticket offices. The monorail(单轨铁路) travels through central Sydney. It is the most excellent way to gain a good view of the whole city. The monorail runs every three to five minutes, and it takes 15 minutes to complete its journey.

    Sydney is built around a harbor, and the Parramatta River has a large ferry（渡轮）system. It serves the area around the harbor. These include Taronga Zoo, Darling Harbor, Rose Bay, the North Shore, Cockatoo Island and Sydney Olympic Park. The ferries have operated for more than 135 years and 14 million passengers take the ferries each year.

    Water taxis can transport passengers to specific locations(地点), and offer guided tours of waterways. They also offer special services that some visitors may enjoy. The tickets sell for 20 AUD (Australian dollars)for a day or 57 AUD for a week. It is strange, isn't it?

New Schedules（日程/安排）of Cathay Pacific Airways(航班)

(注：Dep.为Departure的缩写，意为“离开”；Arr.为 “Arrive”的缩写。)

    Six months after a Chinese scientist was widely condemned for helping to make the world's first gene­edited babies, he remains out of public view, and new information suggests that others may be interested in undertaking the same kind of work outside the United States.

    A clinic in the United Arab Emirates city of Dubai emailed scientist He Jiankui to seek training in gene editing, Stanford University bioethicist Dr. William Hurlbut said ahead of a speech Tuesday at the World Science Festival in New York.

    Hurlbut, whose advice He often sought, said He told him that scientists from multiple countries and families with inherited health problems had messaged support and interest in altering the genes of embryos(胚胎)to prevent or treat disease. Hurlbut gave The Associated Press the email the Dubai clinic sent to He in December but decided to hide the clinic's name.

    "It reveals what eagerness there is out there to use this technology" and the need "for some sort of practical governance" of it, Hurlbut said.

    Jennifer Doudna, a University of California, Berkeley, co­inventor of the CRISPR gene­editing tool that He used, said that she also has heard of others who want to edit embryos.

    "I think they're entirely credible," she said of such reports. Doudna, who was also a speaker at the New York festival, said the field needs to focus on setting specific principles for how and when such work should proceed.

    "The technology is frankly just not ready for clinical use in human embryos," although research should continue, she said. Doudna is paid by the Howard Hughes Medical Institute, which also supports AP's Health and Science Department.

    Scientists and policy leaders have been debating how to set international standards or controls since He claimed in November that he had altered the genes of twin girls at conception(怀孕)to try to help them resist possible future infection with the AIDS virus.

    Editing embryos is outlawed in many countries because it risks damaging other genes, and the DNA changes can be passed to future generations. Many scientists have condemned He's work, and attention has fallen on other scientists who knew or strongly suspected what He was doing.