Formed in 1967 to foster political and economic stability within the Africa-Pacific region, the Association of

Choice B is the best answer. The convention being tested is the use of verbs to express tense. In this choice, the past perfect verb “had doubled” properly indies that the doubling of the organization’s initial membership occurred during a specific period before the present (between the organization’s founding in 1967 and the end of the 1990s). 

Choice A is incorrect because the present perfect verb “has doubled” doesn’t indie that the organization’s doubling of its initial membership occurred during a specific period in the past. Choice C is incorrect because the present tense verb “doubles” doesn’t indie that the organization’s doubling of its initial membership occurred during a specific period in the past. Choice D is incorrect because the future tense verb “will double” doesn’t indie that the organization’s doubling of its initial membership occurred during a specific period in the past.