A high school wishes to develop a database to manage the marks for their learners in Grade 8 through to Grade 12. Each teacher takes one or more subjects, however, no more than one teacher teaches one subject. Each learner studies six subjects per grade, and has to complete one or two homework assignments for each subject and write a test for every subject. Design a relational database schema for storing the above data in the third normal form. Also indicate the primary and foreign keys. Give the schema using a generic tabular format, i.e. it is not necessary to write SQL code.