The polar bear is found in the Arctic Circle and some big land masses as far south as Newfoundland. While they are rare north of 88°, there is evidence  61   they range all the way across the Arctic, and as far south as James Bay in Canada. It is difficult to figure out a global population of polar bears as much of the range has been  62  （poor) studied; however, biologists calculate that there are about 20,000–25,000 polar bears worldwide.

Modern methods  63   tracking polar bear populations have been employed only since the mid-1980s, and are expensive  64  (perform) consistently over a large area. In recent years some Inuit people in Nunavut 65   (report) increases in bear sightings around human settlements, leading to a  66   (believe) that populations are increasing. Scientists have responded by  67   (note) that hungry bears may be congregating（聚集）around human settlements, leading to the illusion（错觉）that populations are  68  (high) than they actually are. Of  69   nineteen recognized polar bear subpopulations, three are declining, six  70   (be) stable, one is increasing, and nine lack enough data.

According to a review of evidence in a medical journal, runners live three years   61  (long) than non-runners. You don\'t have to run fast or for long  62  (see)the benefit. You may drink, smoke, be overweight and still reduce your risk of    63  (die) early by running. While running regularly can\'t make you live forever, the review says it   64   (be) more effective at lengthening life65 walking, cycling or swimming. Two of the authors of the review also made a study published in 2014  66  showed a mere five to 10 minutes a day of running reduced the risk of heart disease and early deaths from all   67  (cause).

The best exercise is one that you enjoy and will do. But otherwise…  it\'s probably running. To avoid knee pain, you can run on soft surfaces, do exercises to  68  (strength)your leg muscles(肌肉),avoid hills and get good running shoes. Running is cheap, easy and it\'s always  69 (energy).If you are time poor, you need run for only half the time to get the same benefits as other sports, so perhaps we should all give  90  a try.

There has been a recent trend in the food service industry towards lower fat content and less salt. This trend, which was started by the medical community(医学界)  61   a method of fighting heart disease, has had some unintended side  62  (effect) such as overweight and heart disease—the very thing the medical community was trying to fight.

Fat and salt are very important parts of a diet. They are required  63   (process) the food that we eat, to recover from injury and for several other bodily functions. When fat and salt    64 (remove) from food, the food tastes as if it is missing something. As    65   result, people will eat more food to try to make up for that something missing. Even    66   (bad), the amount of fast food that people eat goes up. Fast food  67     (be) full of fat and salt; by  68   (eat) more fast food people will get more salt and fat than they need in their diet.

Having enough fat and salt in your meals will reduce the urge to snack(吃点心) between meals and will improve the taste of your food. However, be  69   (care) not to go to extremes. Like anything, it is possible to have too much of both,  70   is not good for the health.

Chengdu has dozens of new millionaires, Asia\'s biggest building, and fancy new hotels. But for tourists like me, pandas are its top  61  (attract).

So it was a great honour to be invited backstage at the not-for-profit Panda Base, where ticket money helps pay for research, I  62  （allow）to get up close to these cute animals at the 600-acre centre. From tomorrow, I will be their UK ambassador. The title will be  63   (official) given to me at a ceremony in London. But my connection with pandas goes back  64   my days on a TV show in the mid-1980s,  65 I was the first Western TV reporter  66  (permit) to film a special unit caring for pandas rescued from starvation in the wild. My ambassadorial duties will include  67   (introduce) British visitors to the 120-plus pandas at Chengdu and others at a research in the misty mountains of Bifengxia.  

On my recent visit, I help a lively three-month-old twin that had been rejected by  68   (it) mother. The nursery team switches him every few  69 ( day) with his sister so that while one is being bottle-fed,  70 other is with mum-she never suspects.

The adobe dwellings(土坯房) 61.________(build) by the Pueblo Indians of the American Southwest are admired by even 62.________  most modern of architects and engineers. In addition to their simple beauty, what makes the adobe dwellings admirable is their 63.________(able) to “air condition” a house without 64.________(use)electric equipment. Walls made of adobe take in the heat from the sun on hot days and give out that heat 65.________(slow) during cool nights，thus warming the house. When a new day breaks, the walls have given up their heat and are now cold enough 66.________ (cool) the house during the hot day; 67.________ the same time, they warm up again for the night. This cycle  68.________ (go) day after day: The walls warm up during the day and cool off during the night and are thus always a timely offset(抵消) for the outside temperatures. As 69.________(nature) architects, the Pueblo Indians figured out exactly 70.________thick the adobe walls needed to be to make the cycle work on most days.