2．Five tips for safe running We all know that exercise is good for our health．But some kinds of exercise may be better than others．Running，for example，may help to protect against heart disease and other health problems． Running is good exercise，but it can be hard on the body．（36）G Take it easy．Do not run too much，too soon or too fast．Most people get running injuries when they push themselves too hard．The body needs time to get used to increases in distance or speed．（37）E Listen to your body．Most running injuries do not come unexpectedly．（38）B They may include body aches，sore muscles and pain that does not go away． （39）A There is no single best shoe for every runner．You should find the shoe that offers the best fit and support for your feet．More importantly，you should replace your shoes every 500to 800kilometers． Take good notes．Take time after each run to write down what you did and how you felt．Look for patterns（模式），things that happen over and over again．These notes will help you find the best exercise for you． Cross train．As we said earlier，running is hard on your body．So physical fitness experts suggest some form of cross training to improve muscle balance and to help you stay injury free．They say swimming，yoga，and riding a bicycle are good exercises to combine with running．（40）D
A．Get good running shoes． B．Usually，there are warning signs． C．Running may also help you live longer． D．These exercises are easier on the body． E．Muscles and joints（關(guān)節(jié)） need time to recover． F．As advertisements for the running shoe Nike say，"just do it．" G．Here are five ideas to reduce the risk of injury．
20．My mother is a diligent and kind woman．She is very busy form morning till night．As a teacher，she works hard．（16）BBoth my brother and I love her dearly as she loves us． My mother has been teaching math at a middle school in my hometown．She goes to work early in the morning and does not return home until late in the afternoon．（17）C She treats them with patience and teaches them well．For her excellent quality and very good teaching results，she has been elected as a model teacher several times． （18）EEvery day，when she comes back home from work，she sets about doing housework，sweeping the living room and bedrooms or cleaning the furniture，and putting everything in good order．She seems to be busy all the time．As she has been very busy working every day，she looks older than her age．But she looks as cheerful and happy as ever．Mother never buys expensive dresses for herself，but she often buys some inexpensive but high quality clothes for us．（19）D She just eats a plain meal outside when she is too busy to cook herself．She lives a busy yet simple life，without any complaints． Often she says to us，"work while you work，and play while you play．That is the way to be happy and gay．If you do not work，you will become lazy and be of no use to society"．What a piece of good advice this is!（20）FThis advice of hers will always serve as a guide to my behavior．My mother is great indeed，and I always feel proud of her．
A．She enjoys listening to classic music． B．As a mother，she takes good care of us and gives us every comfort． C．She loves her students and cares for them． D．She never goes to expensive restaurants to enjoy meals． E．My mother is hard-working and never wastes money． F．I never forget it and always bear it in my mind． G．Can you tell us something about your mother？
1．（36）B．Scientists have learnt that Mars seems to be the planet with the best conditions for life after Earth．（37）E．The reason is that the air on Mars is mainly made up of carbon dioxide，nitrogen，and argon，all of which humans cannot breathe，and has only 0.13% oxygen，while the oxygen content of the air on Earth adds up to 21%． （38）D．We now know there isn't enough oxygen on Mars for humans to breathe，but there are signs of water there．NASA scientists have found ice on Mars，and there is some water in the atmosphere．The Phoenix Mars Lander landed on the planet on May 25，2008，to find out if there was life there，and to explore the planet's climate and geology．（39）G．A physicist once said，"We agree that life can exist under different conditions．We now believe that there might have been some form of life on Mars billions of years ago，maybe deep underground．（40）F．On the question of humans going to live on Mars-well，first of all，we have to sort out some problems．And then…who knows？"
A．The physicist is not sure whether people will live on Mars one day． B．Whether life can exist on Mars has been a question in the minds of experts for a long time． C．Humans can't breathe on Mars because there is too little air there． D．As far as we know，for life to exist，two essentials are needed-air and water． E．However，if people went to live on Mars tomorrow，they won't be able to breathe． F．Personally，I think that if we knew where to look，we would find life on Mars today． G．The information that it sends back will help us prepare for sending people to explore Mars in the future．
