Responsive GPT Ads: Best Practice?

Not sure where to start with this research so I'm starting here.

I'm currently using the 7.x module on a site that is switching to the Bootstrap theme. One of the main challenges has been how to setup responsive ads using Google Ad Manager's Order System and Drupal's DFP module. So without further adieu...

#1) Is this still the correct module to be using to integrate Google Ad Manager ads into Drupal 7?

#2) What is the preferred/correct way to display the right size creative depending on the device being used?

I've come up with a few possible ways to do it, but I'm not sure what, if any, is the suggested practice.

A) Create multiple Inventory spots for the same location on the website then show/hide them depending on the device using Bootstrap CSS. This seems excessive from a site loading time point of view.

B) Create an Order in Google Ad Manager, add multiple creatives for different sizes, then somehow have my DFP Tags on the Drupal site know which creative to pick. So far I've not gotten this to work. I'm thinking I don't have the breakpoints set correctly in the DFP Tag, but I haven't found any current documentation to clear things up.

C) Create Inventory spots for every desktop and mobile ad location. Then create orders in Google Ad Manager and target each creative to a specific Inventory spot. Seems like a lot of setup but might be the 'easiest' route.

Are any of these on the right track? I'm open to suggestions! Thanks in advance!