What (qué) – What are you doing?

Where (dónde) – Where did you go on vacations?

When (cuándo) – When is your birthday?

How (cómo, cuán) – How was the party?

Why (por qué) – Why are you mad?

Which (cuál, cuáles) – Which car would you like to buy?

Who (quién, quiénes) – Who is your best friend?

Whom (a quién, a quiénes) – Whom are you sending the letter?

Whose (de quién, de quiénes) – Whose book is that?