With a great many verb-preposition combinations, English allows the placement of the preposition either before the relative pronoun or at the end of the clause. The first of these is the more formal and so in some cases may be deemed preferable. (Shun as a pedant anyone who tells you that the second is always to be avoided!) Examples:

• The house in which I live (that I live in) was built in 1930.
• The topics about which we are talking (that we're talking about) are controversial.

In Spanish, no such choice exists. The preposition must be placed before the relative:

• La casa en la que yo vivo fue constuida en 1930.
• Los temas sobre los que estamos hablando son controversiales.