To solve this question, the user needs to know about Visual Basic web form code files and their extensions.

The extension for a Visual Basic web form code file is typically ".aspx.vb". This file contains the code-behind logic for a web form created using Visual Basic.

Now, let's go through each option and explain why it is right or wrong:

A. .asp: This extension is used for Active Server Pages, which is a server-side scripting language used to create dynamic web pages. It is not the extension for Visual Basic web form code file.

B. .aspx: This extension is used for Active Server Pages.NET, which is a web application framework developed and marketed by Microsoft to allow programmers to build dynamic web sites, applications and services. It is not the extension for Visual Basic web form code file.

C. .asp.vb: This extension is not typically used for Visual Basic web form code file. It is not the correct answer.

D. .aspx.vb: This extension is the correct answer. This is the extension used for Visual Basic web form code file which contains the code-behind logic for a web form created using Visual Basic.

E. .asp.vb.net: This extension is not typically used for Visual Basic web form code file. It is not the correct answer.

Therefore, the answer is: D. .aspx.vb