Spanish language Q&A Forum

Could you please explain further why "cuál" is used instead of "qué" in these examples? 

In your example on the use of tanto...como, one of your sentence  has left me uncertain about the translation. Tanto cuando son pequeños como majores, los hijos siempre preocupan a los padres. The English translation in your example is: Whether they are young or grown-up, children are always a worry for their parents. The use of the personal "a" before the word "los padres" suggests that the children worry about the parents, except that the verb should have been "se preocupan"..If it was intended to mean that the parents always worry about the children whether young or grown-up, in my opinion, the words "los hijos" and "los padres" should be interchanged, with the verb se preocupan. Otherwise  " están ocupados" should have been used instead of "preocupan"  and or used before los padres. Please advise.