These sentences talk about masculine plural nouns. Let's listen. Los niños son inteligentes. The children are intelligent. Now, niños could be all boys or it could be boys and girls. If I said the word niñas with an a, niñas that would be all girls. There's an important distinction. When we have a noun in plural, that is in masculine, it could both mixed gender or just masculine. The only way to have all feminine plural is if you have "as" like niñas. So, let's do these masculine plurals again. Let's repeat. Los niños son inteligentes, Los accidentes son terribles, Los teléfonos son importantes, Los aeropuertos son necesarios. Did you notice that to make a generalization you need to have article "Los" or "Las." This is different from English. In English I say, "airports are necessary." But in Spanish, you need to say, Los aeropuertos son necesarios.