How to display some sitebox only on certain category or product page?

I mean, if I have category A and category B.

I want to put some common content on all category A products info page.
Like, I have 50 products added in category A, and in each product info page, there are some common content and may need modification frequently. I want to add a 'include(***)' code between description and attributes.

I know there are kind of code called 'case .....'. I don't know how to use it.

like:
in tpl_product_info_display.php

add:
case category ID = A
include(productadditionalinfoA.php)
case category ID = B
include(productadditionalinfob.php)

I don't know how to write these codes correctly.
Please help, Thanks

Never mind, I got it.

in tpl_product_info_display.php

add:

8 is category ID.
something like that.