无法在selenium webdriver中选择自动完成的值表单

Question

WebElement t= driver.findElement(By.xpath("/html/body/div[1]/div[4]/div[1]
/div[1]/div/div/div/fr m/div/div[1]/input"));
t.sendKeys("Boston");
t.sendKeys(Keys.Tab);
t.sendkeys(keys.Arrowdown);
Thread.sleep(1000);

Arrow down无效。但Tab，rightarrow和所有其他键正在运作