Critical Reasoning

Scientists are discussing ways to remove excess carbon dioxide from the atmosphere by increasing the amount that is absorbed by plant life. One plan to accomplish this is to establish giant floating seaweed farms in the oceans. When the seaweed plants die, they will be disposed of by being burned for fuel.

Which of the following, if true, would indicate the most serious weakness in the plan above?
A. Some areas of ocean in the Southern Hemisphere do not contain sufficient nutrients to support large seaweed farms.
B. When a seaweed plant is burned, it releases an amount of carbon dioxide comparable to the amount it has absorbed in its lifetime.
C. Even if seaweed farms prove effective, some people will be reluctant to switch to this new fuel.
D. Each year about seven billion tons of carbon dioxide are released into the atmosphere but only about five billion tons are absorbed by plant life.
E. Seaweed farms would make more money by farming seaweed to sell as nutritional supplements than by farming seaweed to sell as fuel

[spoiler]why E? for me, E is out of scope... the problem about if farm makes more money by farming seaweed is not mentioned and cared in the text.....
B is my answer[/spoiler]