I suppose the 'string' is an instance variable in object C, and that there is only one object C. If there are more instances of object C, you have to explain wich instance of object C must be picked.
I suppose the string is made and present.
Then (under those circumstances) ....
Trigger for Instance of Object B's tween ended ... sets that that object picked.
There is only 1 instance of object C .. so it does not need picking.
In a sub, evaluate the instance variable of Object C with the string in Object B.
If not true, reset B, it does not need picking.
For the others the easyst thing is to use a Function. Because Functions start picking from scratch.
So, if the evaluating condtion is not true, ....
call a function 'send all B back". In that on function you dont need to pick, just the action to send B back. (when not picked, actions adress all B's)
call a function 'reset all A". In that on function you dont need to pick, just reset A (when not picked it resets all A)
Hope that is clear.