Question

las/los ______ son las ruedas de una grúa con ranuras abiertas en las que encajan las cuerdas o los cables. barandas superficies de apoyo indicadores de momento de carga poleas

Explanation:

• "Barandas" means "railings" and has no relation to crane wheels.
• "Superficies de apoyo" means "support surfaces" and is not relevant to the described crane wheels.
• "Indicadores de momento de carga" means "load moment indicators" and is not the correct term for the described crane wheels.
• "Poleas" means "pulleys" which are wheels of a crane with open grooves where ropes or cables fit.

Answer:

Poleas