II.Choose the word whose main stress is placed differently from the others in each group:
1/A. headmaster B. holiday C. attractive D. internet
2/A. matter B. happen C. listen D. below
3/A. explain B. problem C. study D. worry
4/A. habit B. become C. learner D. mother
5/A. fifteen B. fifty C. center D. biggest
6/A. student B. member C. prefer D. teacher
7/A. subject B. hello C. teacher D. thousand
8/A. lesson B. woman C. repair D. father
9/A. above B. sister C. widen D. very
10/A. corner B. answer C. doctor D. prepare