7,000,000,000 * 150 pounds = 1.05 * 10^12 pounds = 4.7 * 10^11 kilograms
Checked statistics for world population in 2013 and average weight of a human. . .
7,100,000,000 * 137 pounds = 9.727 * 10^11 pounds = 4.41 * 10^11 kilograms
If you're using pounds, then the answer looks like it's somewhere between d) and e)
If you're using kilograms, then the closest answer looks like it's d)