Switch choices occasionally (2,3,3)
I believe the answer is:
on and off
I believe this is a double definition.
'switch choices' is the first definition.
(I've seen this before)
'occasionally' is the second definition.
(I've seen this before)
(Other definitions for on and off that I've seen before include "Occasionally" , "Perhaps switch positions" , "Now and then, starting and stopping" , "From time to time, not continually" , "Intermittently" .)