There might be as many as 10 million species of complex life on this planet today —— a huge number. But add up all of the complex species that ever lived and some biologists think the grand total would be about five billion. The estimate leads to an astonishing conclusion: a staggering 99% of species are not around any more. They have been driven to extinction.

    More species are joining the ranks of the extinct every year. Many scientists believe we are living through an episode of remarkably rapid extinction, on a scale that has been seen only five times in the last half a billion years.

    They call this current episode the sixth mass extinction —— a large, global decline in a wide variety of species over a relatively short period of time. And they tend to agree that humans are the main cause.

    Over-hunting, overfishing, and human-driven habitat loss are pushing many species to the brink. In fact, we have changed the planet so much that some geologists are now suggesting that we have entered a new phase in Earth's history; an epoch they call the ＂Anthropocene＂. By 2100, it is expected that humans will have caused the extinction of up to half of the world's current species.

    Because we are living through this extinction, it is relatively easy for us to study the driving forces behind it. But how do we determine what caused other mass die-offs that happened long ago? To do so we have to look at what archaeologists, palaeontologists, geologists and other scientists have concluded from the evidence they have gathered.

    The trouble is, those scientists do not always agree with one another —— even about the most recent extinction event. As well as the five-or six- mass extinctions, there have also been many smaller extinctions.

    One of these mini extinction events happened towards the end of the Pleistocene, a few tens of thousands of years ago. It is sometimes called the ＂megafaunal＂ extinction because many of the species it claimed were particularly large animals, weighing more than 97lb (44kg). However, its cause remains a debate amongst scientists.

在气垫导轨上，一个质量为600g 的滑块以15cm/s的速度与另一个质量为400g、速度为10cm/s并沿相反方向运动的滑块迎面相碰，碰撞后两个滑块粘在一起，求碰撞后滑块速度的大小．

已知函数$f\left(x\right)=\left|lgx\right|$，若$0<a<b$，且$f\left(a\right)=f\left(b\right)$，则$a+2b$的取值范围是(   )

                                                                           Ways to Free Your Mind You're Feeling Stuck

    Have you ever like you were racing around in without making much forward progress? If you're stuck and you don't know how to rise, don't look outside yourself. Look below.____

    Go back to what's important

    When we get stuck, it can be extremely useful to come back to these three things: core values, beliefs and goals. Why?____

    Ask for help

    Very often, highly happy and successful people have a supporting group of friends, family and others who help them____And don't be afraid to reach out and help someone who's even more stuck than you.

    Embrace the natural pathways

    When you get stuck, there's no need to go back to the drawing board. Ask the people around you about the systems that are working for them, read insightful books and blog articles, and use the same methods and pathways that others have used to get unstuck.____

    Relocate yourself to an inspiring environment

    ____You can go for a walk in a nearby park. You can come out of the office for a cup of coffee. Or if you are at home, you can simply go to a different room in the house. Whether it's urban spaces, parks, libraries, museums or even our own backyards, there are plenty of available sources that we can draw inspiration and strength from.

A. Goals are the outcomes in life that we strive for.

B. Here are some useful ways to help yourself get unstuck.

C. When you are stuck, don't be afraid to ask for help.

D. One way to get unstuck is to simply change your environment.

E. Because they form the basics of what is important to us as individuals.

F. Break the circle of worry and work on something else.

G. In fact, the system is nothing more than a natural pathway of thought that someone has created with their mind.