Why do sedimentary rocks have layers?

What would be a clearer way of writing the sentence below? for the students' new project, the students will write a report about a book, and they will read the report to the other students in the class; also, the reports must be completed so that they can be read to the class on december 18. a. for their new project, the students will write a book report and read it to the class on december 18. b. the students have a new project, and they will have to write a book report and read it to the class. c. students must read a book and then write a report over the book they read, and they must read the report they wrote to the class. d. on december 18, the students in the class will read stuff to each other because that is the day their project is due.