Tenemos que decidir cuál de los dos proyectos vamos a llevar a cabo. - No entiendo por qué no ambos.We have to decide which of the two projects we're going to carry out. - I don't understand why not both.
Solo vamos a visitar uno de los dos países. - ¿Y por qué no ambos? Están uno junto al otro.We're only going to visit one of the two countries. - And why not both of them? They're next to each other.