单项选择题 A Web page includes the HTML shown in the following code segment.  You need to write a JavaScript function that will dynamically format in boldface all of the hyperlinks in the ref span.Which code segment should you use？（）

单项选择题 You create a Web page that contains the following image element. You need to write a JavaScript function that will dynamically change which image is displayed. Which code segment should you use?（）

单项选择题 You create a Web page that contains drop-down menus that are defined by using div tags in the following code.  You need to write a JavaScript function that will enable the drop-down menus to activate when the user positions the mouse over the menu title. Which code segment should you use？（）