“出席—缺席”和“出口—进口”“出席”和“缺席”，在语义上正好相对应。但是在语法上，可以说“出席了这次会议”，却不能说“缺席了这次会议”，并不对称。“进口”和“出口”在语义上也是对称的。但是可以说“出口欧美许多国家和地区”，不能说“进口欧美许多国家和... “Attendance - Absence” and “Export - Import” “Attendance” and “Absence” correspond exactly semantically. However, in terms of grammar, it can be said that “we are attending this meeting” but we can not say that we were “absent from this meeting” and that it is not symmetrical. “Imports” and “exports” are also semantically symmetrical. However, it can be said that “exports to many countries and regions in Europe and America” ​​can not be said to "import many European and American countries and ...