Many of us like to think our dogs are smart, as we point to their ability    1    (read) our facial expressions and understand    2    we say. But some dogs are    3    (except). Chaser,    4    American border collie could recognize and remember 1,022 nouns — one for each of her    5    (toy).

The scientists recruited dog owners and asked them to play fetch with their dogs    6    (day) in their homes while    7    (repeat) the name of the toy, a process    8     lasted three months. Dogs that succeeded    9    (give) a new toy and new name to learn. Despite the intensive training, only one dog, Oliva, learned to match a single word to a toy. In fact, she learned 21 names in two months. It’s    10    (interest) that except Oliva, none of the breeds learned a thing. It was such a surprise.

Our emotions have everything to do with our skin. As our largest organ, our skin “gives us away”—what we’re thinking and going through, and     1     we’re feeling. Some examples we are all familiar with are work stress     2     (lead)to acne (痤疮)breakouts and anger increasing the wrinkles on our faces. But what’s the science behind this? If you’re feeling stressed, your body produces     3     chemical that harms facial skin cells by weakening and constricting(收缩)facial blood vessels(血管),     4     leads to poor circulation, decreasing blood supply to the skin, and     5     (eventual)resulting in dry skin. If you have     6     (exist)problems like acne, stress can     7     (worse)them. Stress also results in quicker and shallower breathing, reducing the oxygen carried in your blood stream and by extension reducing the oxygen supply to your skin. As a result, the     8     (health)glow of your skin may disappear.

Also, we are all too familiar with turning to unhealthy food like fatty and sweet junk food when stress hits. Such foods     9     (associate)with acne breakouts. Lastly, sleep may be affected during periods of stress. When this happens, you may wake up     10     baggy eyes, dark circles and dull skin.

There are certain things on the Earth that we must not lose. The great animal migration across the Serengeti Plains or the towering pyramids of Egypt are such examples. Every country is proud of     1     (it) cultural or natural heritage sites,     2     must be protected. We are lucky to have UNESCO to oversee such an important task. It sees heritage as our legacy from     3    past, what we live with today, and what we pass on to future generations as well as sources    4    irreplaceable inspiration.

The incredible splendour of heritage sites is a     5     (remind) of the power of nature and the genius of man. As a nature reserve, Jiuzhaigou Valley is home to snow-capped mountains, thick forests, impressive waterfalls and lakes. This dream-like scenery makes us realize that nature has    6     (true) created a masterpiece. Similarly, standing in the shadow of the Borobudur Temple, as the sun rises over this grand historic building, we    7     (impress) with the effort and determination of the people who     8    (build) it with only primitive tools.

It is in heritage sites like this     9     we cannot help but be humbled, come to understand our limitations as human beings, and know that our duty is to protect them for generations     10     (come).

Back in    1    late 1700s, long before people understood the reason behind immunity (免疫),farmers and doctors in rural areas of Britain noticed that dairymaids(牛奶工) and other people who got a mild disease called cowpox(牛痘) seldom caught its fearsome cousin, smallpox (天花). Was there a connection? Some decided there was an inserted (植入) material from the cowpox into an incision (切口) they cut on the arm of healthy people, thus somehow     2    (protect)them from smallpox. In 1798,a doctor named Edward Jenner published the results of his experiments using this procedure,earning     3    (he)fame as the“Father of Smallpox Vaccination (疫苗接种).”

Scientists later figured out that cowpox somehow protected one from smallpox. When people caught cowpox, their bodies made special cells     4     (call) antibodies. They fought the disease.That's not all. They stayed in the blood       5    case the disease ever returned. Because cowpox and smallpox are fairly similar, if a person was later exposed to the more serious disease, anti-bodies were ready     6    ( fight) it too.

That knowledge helped scientists develop vaccines. The term vaccination was coined from the Latin for cow (vacca).They contain the virus, weakened, dead or modified (改良的) . Injected into the blood, they trick the immune system into making antibodies.    7     the body ever meets with those same    8    (virus),even at full strength,the antibodies make short work of them.

Vaccination prior to     9    (expose) to the virus is ideal. But a vaccination given within three days of exposure will     10    (complete) prevent or significantly modify smallpox in the majority of people and given within the first four to seven days will likely offer some protection or soften the diseases.