For years scientists have been arguing about whether nature or nurture (后天) decides what people will be like. Is it nature— what people are (41) with— that decides what they will be like? (42) is it nurture —what(43) to people when they are born —that decides what they will be like?
Scientists have been studying twins to (44) if they can find the answer, because twins start out with the (45) DNA. Sometimes twins don’t live together at birth and grow up in different (46) and different places— so the nature is the same for both, but the nurture is different.
When scientists (47) these twins in their later life, they some times find some surprising (48).
Jim Springer and Jim Lewis were adopted（收养）by two different families at birth. They first met each other again thirty-nine years (49) and discovered they had a lot in (50). Both had been (51) twice. Their first wives were both named Linda and their second wives were both named Betty!
Each twin had a son — one called his son James Alan and the (52) called his son James Alan, too. Their children each had a dog called “Toy”. They even arrived at their first (53) in the same color of car.
So far twin (54) seem to show that both nature and nurture are important. What we have from birth, and how and where we live help to build (55) we are.

Today some people call Amsterdam the “City of Bicycles” because it is a city which is flat and convenient (方便的) for bicycles.
In the 1960s, a group of cycling fans      an idea. They believed that it would be better for everybody if the city only allows (允许) bicycles to go in the streets in the city centre. They were    that this would help to save energy, reduce pollution and provide free public transport. The group painted hundreds of bicycles       and placed them in public places around Amsterdam for people to use.      could take them and use them for short journeys, whether he was a local or a foreigner. Whenever someone finished a journey, they would    the bike there for someone else to use. The problem was that it didn't work because     took all the bicycles within weeks!
    more than thirty years later, the “white bike” is back in town---this time with a computer chip (芯片) to  its      very move! To take a bicycle, you have to put a special card inside. The new “white bike” is not white any more but is an unusual       with bright colors. The bikes are parked at special parking places and people who want to use them have to take them to another place that has enough room.
There is already less traffic in central Amsterdam, because both locals and tourists are      the white bikes every day. Thanks to the good ideas of lots of people, like the cycling fans in the 1960s, many people around the world have been enjoying city centre streets without cars for many years.