1. El perro grande me gusta más que el pequeño.
(A large dog lies in front of a small dog.)
We know that we are talking about dogs, but the sentence in Spanish does not include the word dog. Perro (dog) is the missing word. Remember that in Spanish the adjective goes after the noun.
2. Se prohíbe alimentar (feed) a los animales .
(A man in the jungle hands a pretzel to a monkey.)
Since the man gives the monkey a pretzel, we can assume that the sentence would be talking about animals (animales).
3. En el centro del estanque (pond) hay un pájaro.
(Five birds drink and bathe in a small pond.)
We know there are five birds in the pond, so the word pájaro (bird) makes the most sense.
4. Hicieron un picnic en un campo rodeado (surrounded) de montañas.
(A man and women sit in a field having a picnic with a lake and mountains in the distance.)
They had a picnic en el campo (a field). We could also use una cancha.
5. ¿Cuál es tu opinión sobre el uso de la energía fósil ?
(A factory with three large smoke stacks.)
Smoke stacks would be an example of fossil fuels, so the most appropriate answer would be energía fósil (fossil fuel).