Three ________ witnessed the traffic accident. A: passer-by B: passer-bys C: passers-by D: passers-bys

All the _____ were shocked at the sudden accident. A: passer-bys B: passers-bys C: by-passers D: passers-by

Please feel free to ask the ______ in the city, if necessary. A: passers-by B: passer-by C: passer-bys D: passers-bys