Mark the letter A, B, C, or D to indicate the word that differs from the other three in the position of the primary stress in each of the following questions. 
1: A. control B. exchange C. focus D. install
2: A. upload B. prepare C. discuss D. textbook
3: A. digital B. schedule C. strategy D. distraction
4: A. digital B. personal C. excellent D. effective
5: A. similar B. national C. effective D. interesting
6: A. exercise B. volunteer C. national D. interview
7: A. balance B. issue C. panda D. extreme
8: A. serious B. influence C. energy D. pollutant
9: A. promote B. support C. research D. nature
10: A. aware B. protect C. impact D. danger
11: A. solution B. habitat C. endangered D. awareness
12: A. natural B. chemical C. atmosphere D. solution
13: A. profit B. protect C. local D. impact 
14: A. ecotourism B. relaxation C. preservation D. disappointed
15: A. tradition B. stalactite C. cultural D. industry