Creo que las hamburguesas son _____ para la salud.
Answer: horribles
Entire sentence: Creo que las hamburguesas son horribles para la salud.
Translation: I think hamburgers are horrible for health.
Explanation: "Horrible" is a Spanish, qualifying adjective and has to agree on gender and number with the noun it qualifies. As "hamburguesas" is a feminine, plural noun, the adjective must agree, but the adjective "horrible" has no a specific gender in Spanish, so it only needs to agree in the plural with the noun. "Hamburguesas horribles".
