Answer:
Zack should update the site using a single W3C language standard conistently, such as HTML5 or XHTML.
Step-by-step explanation:
Because XHTML is a combination of HTML and XML, whereas HTML5 is a version of HTML. XHTML has its own parsing requirements while HMTL does not have any specific requirements and uses its own. HTML5 has a simpler charset and does not need to add type attributes and style elements.