The earth’s resources are being depleted much too fast. To correct

The argument and all the options are rather vague. I don't see it as a GMAT-relevant CR question. But if you must evaluate it, here goes:

Rate of depletion is high in the world.
Conclusion: To correct this, US must consume at same rate for many years to come.
Conclusion refers to US whereas the premises talk about depletion in the world. We need to say why US is singled out to consume responsibly.

(A) New resource deposits are constantly being discovered.
Reduces the need to worry about rate of depletion. Weakens our argument.

(B) The United States consumes one-third of all resources used in the world.
It says that US plays a big role in depletion. Hence, if US becomes responsible, it will make a difference.

(C) Other countries need economic development more than the United States does.
A new parameter - economic development - is introduced. How this links with use of resources, we cannot say. Is economic development stalled if rate of resources used does not increase? Can we not increase efficiency? This is irrelevant to our argument.

(D) Other countries have agreed to hold their resource consumption at present levels.
Currently depletion is happening very fast. If other countries have agreed to hold the consumption at present levels, then it may not matter whether US is holding its consumption at the present level too. I understand the problem many of you are facing. But note that we do not know what "to correct this" means in the argument. Does it mean to "hold the depletion rate" or to "reduce the speed though increased depletion is fine" - we don't know. That is why I said that the argument is just too vague.

(E) The United States has been conserving resources for several years.
If US has already been conserving resources, it holding consumption steady may not make any difference.

So (B) might be the best out of the given bad choices.