Each year {#blank#}1{#/blank#}(thousand) of tourists visit the polar regions of the Arctic and Antarctica. But the increasing number of people traveling to the ends of the Earth can have {#blank#}2{#/blank#}negative effect on fragile ecosystems. Should tourists {#blank#}3{#/blank#}(allow) to visit polar regions?

    About 40,000 tourists visit Antarctica each year. More than five million travel to the Arctic and sub-Arctic. Transporting tourists to the regions {#blank#}4{#/blank#}(increase) ship and airplane traffic, adding to the risk of pollution, oil spills, and other {#blank#}5{#/blank#}(environment) damage. Because the places where wildlife is accessible {#blank#}6{#/blank#}(be) few in number, tourist traffic can become concentrated in specific areas, {#blank#}7{#/blank#} (put)Arctic vegetation at risk.

    Others say that access {#blank#}8{#/blank#}these very special parts of the world should not be restricted to only researchers and scientists. Polar tourism allows people to develop deep  {#blank#}9{#/blank#}（person） connections with polar regions. “Those {#blank#}10{#/blank#}travel to the Arctic or Antarctica often become cheerleaders for supporting those places.” Jim Sano, vice president for travel and conservation at World Wildlife Fund, told TFK.

    There are two main {#blank#}1{#/blank#} (reason) why the temperature of the air is always {#blank#}2{#/blank#} (change). One reason is that the air around you {#blank#}3{#/blank#} (move) in from somewhere else. Air usually moves in large bodies {#blank#}4{#/blank#} (call) air masses. Some air masses move in from the north. These air masses usually have cold air that causes the temperature {#blank#}5{#/blank#} (drop). Air masses also move in from the south. They usually have warmer air that causes the temperature to rise.

    Temperature changes during the day or night can be great {#blank#}6{#/blank#} small. This depends{#blank#}7{#/blank#} (part) on how many clouds are in the sky. {#blank#}8{#/blank#} there are many clouds during the night, they act like covers on your bed. They blanket the earth and keep the air from {#blank#}9{#/blank#} (lose) much of its heat. The temperature usually does not drop much during such a night. When there are many clouds during {#blank#}10{#/blank#} day, some of the sun's energy will not reach the earth. The temperature usually does not rise much on such a day.

    Many years ago, when I worked as a volunteer at Stanford Hospital, I got to know a little girl {#blank#}1{#/blank#}(name) Liz who was suffering from a rare and serious disease. Her only chance of recovery appeared to be a blood transfusion（输血）{#blank#}2{#/blank#}her 5-year-old brother,{#blank#}3{#/blank#} had miraculously survived the same disease and had developed the antibodies needed to fight the {#blank#}4{#/blank#}(ill).

    The doctor explained the situation to her little brother, and asked the boy if he would be willing to give his blood to his sister. I saw him hesitate for a moment {#blank#}5{#/blank#}taking a deep breath and saying, “Yes, I'll do it {#blank#}6{#/blank#}it can save Liz.”

    {#blank#}7{#/blank#} the transfusion progressed, he lay in bed next to his sister and smiled, as we all did, {#blank#}8{#/blank#}(see) the color returning to her cheeks. Then {#blank#}9{#/blank#}face grew pale and his smile faded. He looked up at the doctor and asked with a trembling voice, “Will I start to die right away?”

Being young, the boy had{#blank#}10{#/blank#}(understand) the doctor; he thought he was going to have to give his sister all of his blood.