Which sentence is​ correct?



a. the school system comprises five different​ districts, each of which is comprised of six or more schools.



b. the school system comprises five different​ districts, each of which comprises six or more schools.



c. the school system composes five different​ districts, each of which is comprised of six or more schools.



d. the school system is composed of five different​ districts, each of which composes six or more schools?