定位下拉框，查看HTML，带有select标签
//下拉框选择上海
WebElement province = driver.findElement(By.cssSelector("select[id='companyprovince']"));
Select selectProvince = new Select(province);
selectProvince.selectByVisibleText("上海");
select.selectByValue("2");
select.selectByIndex(2);
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selectByValue：参数为option中的value属性
selectByIndex：参数为option的顺序
selectByVisibleText：参数为option的text值