Nice try, but wrong.
There's nothing written wrongly in the question.
Well, my next best guess is Toh Tuck Avenue... but 173 is
nolonger operated by SMRT. Likewise for 106...
Nonetheless, 963 is still operated by SMRT.... only 106, 173 and
963 actually ply the entire Toh Tuck Avenue in both
directions...
Actually, B can only be 173, 61 or 970. I have looked through
all of SMRT's trunk routes. Only they actually run into SBS
territory AND make U-turn at non-looping point...
That's why I ask if you got write anything wrongly. Well, if no,
then I really do not know the answer.