a. are places where huge amounts of felsic magma have been erupted or intruded. b. represent special events in the Earth's history that may have been caused by superplume activity. c. erupt magma with high viscosity and are therefore localized but very thick. d. occur only along continental margins.

Answerseafloor spreading;

Well, a and b together would be negative. b alone would also be negative.

Many foreign companies buy/build hotels in areas therefore most of the profit from tourism goes to these companies rather than the local economy or local people. 
also, these foreign companies might only employ foreign workers with experience meaning they receive more pay whereas local people would be employed for low skilled jobs and lower pay. 

thats all i can think hope it : )