Crossword Puzzle Office activity

Clue: Office activity

Post office activity, or a hint to this puzzle's theme (LETTERSORTING with 13 letters)
Versatile gym activity (CROSSTRAINING with 13 letters)
Some police officers: Abbr. (e.g. DETS with 4 letters)
Decennial govt. activity (USCENSUS with 8 letters)
Send from office (OUST with 4 letters)
Office stations (DESKS with 5 letters)
Fix, at the vet's office (SPAY with 4 letters)
Show-and-tell activity (EVINCING with 8 letters)
Underworld offices (LAIRS with 5 letters)
Four- or five-star officer (ADMIRAL with 7 letters)