All the cyclists in this club train before sunrise. Complete the next sentence with the standard simple-present form of train, keeping the relative clause about all those cyclists: Mara is one of the cyclists who ___ before sunrise.

Explication

Train is plural because the prompt explicitly makes the relative clause describe all the cyclists, so its antecedent is the embedded plural noun phrase. Trains can be defensible when who attaches to the whole phrase headed by one, but that reading is excluded here; the other forms miss the requested simple present.