22. a. worry  b. enjoy  c. practice  d. visit 

23. a. corner b. opinion c. literature d. household 

24. a. attention b. party c. program d. physics 

25. a. geography b. memory c. difference d. subject 

26. a. entertain b. remember c. improve d. decide 

27. a. scientific b. impossible c. mathematical d. educational 

28. a. determine b. obtain c. harbour d. award 

29. a. atomic b. tragic c. extreme d. professional 

30. a. radium b. tutor c. research d. institute 

31. a. mature b. difficult c. brilliant d. physical
Choose the word whose main stress is placed differently from the others.