Поставьте следующие существительные во множественное число:
school, student, teacher, grade, mark, lesson, class, board, dean, professor, test, examination, classroom, building, hall, computer, calculator, copy, handout (раздаточный материал), pen, crayon (фломастер), pencil, book, library, graduate (выпускник вуза), school-leaver (выпускник школы), undergraduate (студент вуза), principal (директор школы), vice-principal (завуч), meeting, parent, report, certificate, plane, session, office, job, wish, monitor, photo, match, university, floor.

schools, students, teachers, grades, marks, lessons, classes, boards, deans, professors, tests, examinations, classrooms, buildings, halls, computers, calculators, copies, handouts (раздаточный материал), pens, crayons (фломастер), pencils, books, libraries, graduates (выпускник вуза), school-leavers (выпускник школы), undergraduates (студент вуза), principals (директор школы), vice-principals (завуч), meetings, parents, reports, certificates, planes, sessions, offices, jobs, wishes, monitors, photos, matches, universities, floors.