Word/Phrase: which is why
Translation: lo cual es la razón
Pronunciation: lo ˈkwal es la raˈθon
This is the reason - Esta es la razón
I didn't understand, which is why I asked - No entendí, lo cual es la razón
He was late, which is why we started without him - Llegó tarde, lo cual es la razón por la que comenzamos sin él
She didn't come, which is why I was worried - No vino, lo cual es la razón por la que estaba preocupado
They didn't finish on time, which is why we had to extend the deadline - No terminaron a tiempo, lo cual es la razón por la que tuvimos que extender la fecha límite