Usage Note
welcher is the question word 'which', inflecting like dieser to give welche, welches, welchen. In statements it can also be a relative pronoun ('which/who'), though the der/die/das relatives are far more common in speech.
Examples
"Welcher Zug fährt nach Köln?"
Natural Translation
Which train goes to Cologne?
Literal Translation
Which train goes to Cologne?

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