Question - RBS vs OBS

I tought I got this one but I did a mistake and I would like to understand the difference..

 

You want to see hierarchical representation of how many welders are working for your compagny in the Welding and Fabraication Department. Which of the following illustrates this information

 

A. WBS

B. Organizational Breakdown Structure ( OBS )

C. RACI Chart

D. Resource Breakdown Structure

OK Got it,

 

they were talking about Department yes but also resources. Where OBS doesnt breakdown till resources

 

thanks

What's the answer to this?

It's a tricky one, the answer is RBS.

 

I think the key to answer it is,  YES it talks about department but it also talk about Ressources, so it goes down to resources, it will be RBS. Because OBS doesnt go down to ressources, it stop at department level