[单选题]15．

正确答案 ：A

asked

[单选题]最早沟通长江水系和珠江水系的人工运河开通于

正确答案 ：C

秦朝

[单选题]AThe undersea world is very beautiful． Now more and more people want to dive in the water to find the secrets there． Scuba diving is a new sport today． It can take you into a wonder-ful undersea world．

正确答案 ：E

they want to find the secrets of the undersea world

解析：21.B【解析】由第一段第二句可知

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