In spanish what rule could explain what makes a sentence grammatically correct or not

Use your knowledge of the imperfect preterit, present, and future tenses to write a post card to a friend in colombia (remember to use all your skills in the three tenses). tell your friend about what you did last summer, what you are doing today and the things you plan to do next fall.

Can somebody me out with this spanish question? completa la oración con la voz pasiva con se. used cars for sale. carros usados. (the answer is not usa los or venta de)

Yo en la biblioteca hasta las cinco de la tarde. a. estarás b. estará c. estaré d. estarán