Rachel carson’s warning in silent spring was focused on
a. overgrazing by livestock
b. global warming
c. the misuse of pesticides
d. fish stock declines

c.  on the misuse of pesticides.

Explanation:

Rachel Carson was an eminent environmentalist in USA. In her book Silent Spring she focused  on the misuse of pesticides. Silent spring suggested that the planetary ecosystem was reaching the limits what it could sustain. She even got threats for lawsuit from chemical industries. She played a vital role in spreading awareness of the environmental pollution.

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.