"They are known by the police."
Translation:Son conocidos por la policía.
What's wrong with my answer? "ellos son conocidos por la policia" (except the missing accent (: )
That looks like the correct answer given, but I don't know how you choose a, del, or por for the preposition phrase, "BY the police." Can anyone tell me a way to know which means the right thing in context, please? ¡Gracias!
It's not wrong and should be accepted. However, it's not necessary nor common to use the subject pronoun in many cases.