seleccionar choose an interogative word from the list to write a question that corresponds with each response
ellos caminan a la biblioteca
To form a question that corresponds to the response "ellos caminan a la biblioteca" (they walk to the library), you would use the interrogative word "¿adónde?" (where to?).
So the corresponding question would be: "¿A dónde caminan ellos?" (Where are they walking to?)