b) Mark the letter A, B, c or D to indicate the word that differs from the other three in the position of primary stress in each of the following questions. 21. A. Celebration B. Contribution C. operation D. remarkable 22. A. recognise B. recollect C. recommend D. understand 23. A. Compose B. recent C. gentle D. stupid 24. A. publish B. rewrite C. study D. practise 25. A. exercise B. decorate C. extinguish D. advertise 26. A. pillow B. alert C. legal D. model 27. A. register B. regular C. request D. reference 28. A. dangerous B. Curious C. suspicious D. numerous 29. A. voluntary B. Compulsory C. necessary D. stationary 30. A. Comfortable B. remarkable C. teenager D. sensible giải thích