The graph at right shows U. S. energy consumption by source from 1980 to 2040 (based on projections). The consumption is measured in quadrillion BTUs or quads (1 quad = 1.055×1018 J). a. What were the three largest sources of U. S. energy in 2013 in descending order? What total percent of U. S. energy do these three sources provide? b. What percent of total U. S. energy is provided by renewables in 2013? c. Which two sources of U. S. energy decline as a percentage of total energy use between 1989 and 2040 (based on projections)? d. How much U. S. energy (in joules) was produced by nuclear power in 1990?