Formed in 1967 to foster political and economic stability within the Asia-Paciﬁc region, the Association of Southeast Asian
Nations was originally made up of ﬁve members: Thailand, the Philippines, Singapore, Malaysia, and Indonesia. By the end of
the 1990s, the organization ______ its initial membership.
has doubled
had doubled
doubles
will double
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 indicates 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 indicate 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 indicate 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 indicate that the organization’s doubling of its
initial membership occurred during a speciﬁc period in the past.