阅读下面短文,在空白处填入1个适当的词或括号内单词的正确形式。
In the year of 1247, Italian explorers Marco and Niccolo Polo set out on{#blank#}1{#/blank#} 24-year journey. During the journey, they traveled the famous SilkRoad from Italy, through terrible deserts and very high {#blank#}2{#/blank#} (mountain) to the eastern China. They traveled over 4,000 miles in all. Marco and Niccolo were among the very {#blank#}3{#/blank#} (one) Europeans to explore the empire of China. In China, Marco Polo even worked {#blank#}4{#/blank#} the ruler Kublai Khan. Polo described his experiences and findings in China by {#blank#}5{#/blank#} (write) a book. Polo described materials and inventions never seen before in Europe {#blank#}6{#/blank#} (careful). Paper money, a printing press, gunpowder and coal were among the products he wrote about. He also talked about the vast wealth of Kublai Khan, as well as the geography of northern and {#blank#}7{#/blank#} (south) China. European rulers {#blank#}8{#/blank#} (be) very interested in the products Polo described. However, trading for them along the Silk Road was {#blank#}9{#/blank#} (danger),expensive and impractical. European rulers began to wonder {#blank#}10{#/blank#} there was a sea route to the East to get the products they wanted at a reasonable price.