Saber is used when speaking of known facts or learned skills, whilst conocer is used to convey familiarity [with something, someone, or some place].
12. Maria knew everyone (she was familiar with them), thus conocer is the correct verb. The conjugation for a singular subject in preterite tense is <span>conocía.
13. "He" (the subject) knows what happened in the movie, he knows the facts of the events that took place. The correct verb here is saber. The singular conjugation of saber in past tense is </span><span>sabía.
14. The student knows the answer (the sentence pertains to known facts); the correct verb is saber. Present tense conjugation of saber for a singular subject is sabe.
15. He is familiar with Bach's music. Familiarity with something uses the verb conocer. The conjugation of conocer for a singular subject in present tense is </span><span>conoce.
16. This question could be asking if you know who is singing (perhaps at an event) or if you are familiar with a person singing. Either verb could work here, depending on the context. There is a clue as to the informality of the context (it uses </span><span>tú and not usted). The question is present tense, so the verb could be either sabes or conoces.</span>
