Interesting how I'm getting downvoted for stating this. The language does come awfully close to explicitly stating just the thing:

"We collect information to provide better services to all of our users – from figuring out basic stuff like which language you speak, to more complex things like which ads you’ll find most useful"

even explained thus:

"For example, if you frequently visit websites and blogs about gardening, you may see ads related to gardening as you browse the web."

and they say that they base it on:

"Information we get from your use of our services."

Again, not explicitly named, but not forbidden either by their own privacy policy.