To write a sub procedure declaration, the user needs to know how to declare a sub procedure in the programming language they are using. The options provided are methods to write a sub procedure declaration in different programming environments.

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

A. Use the Class and Method combo boxes in the Code Editor window. This option is specific to certain programming environments that have a Code Editor window with Class and Method combo boxes. If the programming environment being used provides this feature, then it can be a valid way to write a sub procedure declaration in that specific environment.

B. Double click on the object in the Form Designer window. This option is specific to programming environments that have a Form Designer window. Double-clicking on an object in the Form Designer window can create an event handler for that object, which includes the sub procedure declaration. If the programming environment being used has this feature, then it can be a valid way to write a sub procedure declaration in that specific environment.

C. Type the procedure declaration in the Code Editor window. This option is a general way to write a sub procedure declaration in any programming environment that provides a Code Editor window. The user can manually type the procedure declaration in the Code Editor window, specifying the name, parameters, and return type (if applicable) of the sub procedure.

D. Both a and b. This option is incorrect because it only includes options A and B. Option C is not included.

E. All of the above. This option is incorrect because it includes all options A, B, and C. Option D is not included.

Therefore, the correct answer is:

C. Type the procedure declaration in the Code Editor window.