| 1. | Cities are the defining symbol of modern civilization 城市是现代文明的鉴定标志。 |
| 2. | Undefines all previously defined symbols 取消定义所有先前定义的符号。 |
| 3. | Defines symbols for conditional compilation 定义用于条件编译的符号。 |
| 4. | Undefine previously defined symbols 取消定义先前定义的符号。 |
| 5. | Reopening a method that has been previously closed erases any previously defined symbols for the method 若重新打开以前关闭的方法,则会清除以前为该方法定义的任何符号。 |
| 6. | Reopening a method that has been previously closed erases any previously defined symbols for the method 若重新打开以前关闭的方法,则会清除以前为该方法定义的任何符号。 |