Environmentalists use the metaphor of the earth as a "spaceship" in trying to persuade countries, industries and people to stop wasting and polluting our natural resources. since we all share life on this planet, they argue, no single person or institution has the right to destroy, waste, or use more than a fair share of its resources. but does everyone on earth have an equal right to an equal share of its resources? the spaceship metaphor can be dangerous when used by misguided idealists to justify suicidal policies for sharing our resources through uncontrolled immigration and foreign aid. in their enthusiastic but unrealistic generosity, they confuse the ethics of a spaceship with those of a lifeboat. a true spaceship would have to be under the control of a captain, since no ship could possibly survive if its course were determined by committee. spaceship earth certainly has no captain; the united nations is merely a toothless tiger, with little power to enforce any policy upon its bickering members. if we divide the world crudely into rich nations and poor nations, two thirds of them are desperately poor, and only one third comparatively rich, with the united states the wealthiest of all. metaphorically each rich nation can be seen as a lifeboat full of comparatively rich people. in the ocean outside each lifeboat swim the poor of the world, who would like to get in, or at least to share some of the wealth. what should the lifeboat passengers do? first, we must recognize the limited capacity of any lifeboat. for example, a nation's land has a limited capacity to support a population and as the current energy crisis has shown us, in some ways we have already exceeded the carrying capacity of our land.

which sentence from the passage best states its central argument?

a. a true spaceship would have to be under the control of a captain, since no ship could possibly survive if its course were determined by committee.

b. metaphorically each rich nation can be seen as a lifeboat full of comparatively rich people.

c. first, we must recognize the limited capacity of any lifeboat.

d. since we all share life on this planet, they argue, no single person or institution has the right to destroy, waste, or use more than a fair share of its resources