"El perro bebe agua."
Translation:The dog drinks water.
If I tell you, you can drink the milk= you can drink it all, if you want. If I tell you, you can drink milk, you can drink a part of it or a glass. Do you see the difference?
If you want to generalize, you would be correct, but the lesson is asking for a specific answer. In other sections they ask for you to answer a similar question in a different but specific way. These are lessons. They are showing you subtle differences, all used, but all slightly different. And they want you to do all of them, as they say, so that you expand your hearing and speech!
In English some particulars letters/sounds/syllables in a word are stressed more than others. In Hindi (Indian tounge) all syllables are stressed equally and loud. Which case is it in Spanish?