Explanation
Correct answer: A.
Choice A is the best answer. "In contrast" logically signals that the information in this sentence—that Jordan has yet to officially ratify the treaty—contrasts with the previous information about Niger having already ratified the treaty.
Why the other choices are wrong
Choice B
Choice B is incorrect because "specifically" illogically signals that the information in this sentence specifies or elaborates on the previous information about Niger ratifying the treaty. Instead, the sentence changes subjects from Niger to Jordan, presenting contrasting information about Jordan’s treaty status.
Choice C
Choice C is incorrect because "for example" illogically signals that the information in this sentence exemplifies the previous information about Niger ratifying the treaty. Instead, the sentence explains that Jordan has yet to ratify the treaty.
Choice D
Choice D is incorrect because "similarly" illogically signals that the information in this sentence is similar to the previous information about Niger ratifying the treaty. Instead, the sentence presents contrasting information that Jordan has yet to ratify the treaty.