Solution:(d) "Go straight to your classrooms," the teacher said to the students. (Correct)
(a) "Go straight to their classrooms," the teacher said to the students. (Incorrect Pronoun)
(b) The teacher said to the students, "Please go straight to your classrooms." (Incorrect Word)
(c) The teacher said, "Students, to go straight to their classrooms. "(Incorrect Pronoun & Incorrect Preposition)