The question is asking which of the following is most helpful in achieving responsiveness....
Resposniveness require using one of the newer layout types such as dynamic, column or screen layouts, which is why the answer a is correct.
The second one impacts responsiveness to a certain degree however it does not directly play a role in responsive behavior.... we can enable this field and not use any of the newer layouts, also this field is enabled by default on Pega 7 and is not required to be enabled.
Using auto generated user interfaces again does not indicate responsive behavior if smart layouts or free form layouts are used.
The correct answer is indeed the first one. Using a Stacked Dynamic Layout to group data elements. To make a user interface responsive we need to use the new layouts (Stacked, Inline Grid, Inline, Grid Double, etc). They include options that allow us to set breakpoints in our Skin rules on these layout objects.
The second option does not need to be enabled as it is enabled by default.
The third option does not necesarily make the layout responsive. For example we could use a freeform layout or smart layout and it would still not be responsive as there are no options available in the Skin to set breakpoints on those layouts.