Question

You want to know the reason why, so you ask
a. ¿Dónde?
b. ¿Cómo?
c. ¿Cuál?
d. ¿Por qué?

Answer 1

D. ¿Por qué? Because it is used to ask why (A is used to ask where. Such as "¿de donde eres?". B is used as "how" such as "¿como estas?". C is used as "what", such as "¿cual es tu numero de telephono?") hope this helps!

Answer 2

Por què means why so the answer would be D