As per a report published by the United States Bureau of Economic Analysis, in the last five years, the per capita income of American workers employed in Agriculture and allied services has increased by 10 percent while that of American workers employed in other sectors has increased by 20 percent. Therefore, American workers employed in other sectors now earn a higher per capita income than those employed in Agriculture and allied services.
The argument's reasoning is questionable because the argument fails to rule out the possibility that
A five years ago, fewer American workers were employed in other sectors than in Agriculture and allied services
B five years ago, the per capita income of American workers employed in other sectors was significantly less than that of American workers employed in Agriculture and allied services
C over the last five years, the number of American workers employed in other sectors has decreased
D over the last five years, many American workers who were previously employed in Agriculture and allied services shifted to other sectors
E the total national income generated by Agriculture and allied services now is still greater than that generated by other sectors
Solution:The increase is compared w.r.t previous value(5 yrs ago)
what if the previous value(the per capita income of American workers employed in other sectors ) was way smaller than that with which it is being compared (per capita income of American workers employed in Agriculture and allied services)
for example- a 10 to 15 value increase is 50% increase
while a 20 to 25 value increase is 25% increase
although amount of change in both the cases is of 5 units ,percentage increase is different and depends on original value.hence B is the correct choice.Reward the kudos if you like the explanation.

regards,
Atul Pandey