ⅰ.单词拼写 1.chinese submarine detector jiaolong ________ (延伸) to a depth of over 5,000 meters under the sea. 2.there are few places on the course, so it is essential to ______ (预定) in advance. 3.the latest pop music ________ (进口) from the republic of korea are popular with young people. 4.they built a monument in m______ of a hero who contributed his life to the city.