Enumerate all of the legal clues that Alice can give.
Of these possibilities, what clue should Alice give?
Alice can clue yellow to Bob as a Play Clue on the yellow 3 (through Cathy's yellow 2).
Alice can clue number 3 to Bob as a Play Clue on the yellow 3 (through Cathy's yellow 2).
Alice can clue number 5 to Bob as a 5 Save on the blue 5.
Normally, Alice would prefer to give a Play Clue over a Save Clue. However, in this case, her Play Clue would be a Delayed Play Clue, because Bob would not be able to play the card yet. (Bob would have to wait for Cathy to play the yellow 2.)
So, if Alice gave a Play Clue to the yellow 3, then Bob might have nothing to do and might discard the critical blue 5. This means that Alice must perform some other action.
Thus, Alice should clue number 5 to Bob as a 5 Save.