The stimulus says that the agreement probably would significantly reduce pollution in the world’s oceans. So there’s no basis to believe that the agreement is unlikely to achieve its goal. This is why (A) doesn’t strengthen the argument.

Strengthens the argument by affirming that protecting economic growth is more important than reducing pollution in the oceans. If (B) is true, we have more reason to not sign the agreement.

Wrong trigger. We don’t know whether there is a better way to achieve the goal of reducing pollution in the oceans.

Too weak. (D) supports the idea that we should consider effect on economies when deciding whether to sign an agreement. But we’re trying to reach the conclusion that we shouldn’t sign. Merely taking certain factors into account doesn’t get us to “should not sign.”

(E) allows us to reach a conclusion that a government should implement a policy. But we’re trying to prove that a government should not sign an agreement, which is closer to NOT implementing a policy.