Single out that’s groundbreaking? (4)
I believe the answer is:
pick
I believe this clue is a double definition.
'single out' is the first definition.
(thesaurus)
'that's groundbreaking?' is the second definition.
(a pick might break into the ground)
(Other definitions for pick that I've seen before include "option" , "tool - it breaks" , "Choose - ground-breaking instrument" , "tool for breaking rocks" , "Choose - best" .)