(a) The pupils who are on duty cleaning the classroom. or perhaps; The pupils who are on duty are cleaning the classroom
(b) He keeps his bedroom tidy.
(c) My mother and brother are riding on the elephant.
(d) The duty class is cleaning the classroom.
(e) David is the fattest among all of them.
(f) Davis is the fattest among Chee Hong and Lai Yun.???
(g) They queue up when they are boarding the bus now.
(h) The duty of the students are is cleaning to clean the classroom. suggest; It is the duty of the students to clean the classroom.