stale element reference: element is not attached to the page document

//should set firefox path
        //FirefoxBinary binary=new FirefoxBinary(new File("C:\\Program Files (x86)\\Mozilla Firefox\\firefox.exe"));
        
        //FirefoxProfile profile = null;
        System.setProperty("webdriver.chrome.driver", "e:\\chromedriver.exe"); 
        ChromeOptions options = new org.openqa.selenium.chrome.ChromeOptions();
        DesiredCapabilities capabilities = org.openqa.selenium.remote.DesiredCapabilities.chrome();
        capabilities.setCapability("chrome.switches", Arrays.asList("--start-maximized"));
        options.addArguments("--test-type","--start-maximized");
        WebDriver driver=new ChromeDriver(options);
        driver.get("http://www.tsinghua.edu.cn/");
        //driver.manage().timeouts().pageLoadTimeout(20,TimeUnit.SECONDS);
        //driver.manage().timeouts().implicitlyWait(10,TimeUnit.SECONDS);
        //driver.manage().timeouts().setScriptTimeout(30,TimeUnit.SECONDS);
         
        
        WebElement gaikuang=driver.findElement(By.xpath("//*[@id=‘nav‘]/li[2]/a"));
        
        Actions action =new Actions(driver); 
        action.moveToElement(gaikuang).click().perform();
        List <WebElement> elements=driver.findElements(By.tagName("a"));
         
         for(WebElement e:elements)
            {
                //System.out.println(e.getText());
                //open 现任领导 
                if(e.getText().equals("现任领导"))
                {
                    e.click();
                }
                
            }
     
        
        
         
        driver.quit();