Astronomers are conﬁdent that the star Betelgeuse will eventually consume all the helium in its core and explode in a
supernova. They are much less conﬁdent, however, about when this will happen, since that depends on internal
characteristics of Betelgeuse that are largely unknown. Astrophysicist Saraﬁna El-Badry Nance and colleagues recently
investigated whether acoustic waves in the star could be used to determine internal stellar states but concluded that this
method could not suﬃciently reveal Betelgeuse’s internal characteristics to allow its evolutionary state to be ﬁrmly ﬁxed.
It describes a serious limitation of the method used by Nance and colleagues.
It presents the central ﬁnding reported by Nance and colleagues.
It identiﬁes the problem that Nance and colleagues attempted to solve but did not.
It explains how the work of Nance and colleagues was received by others in the ﬁeld.
Choice C is the best answer because it best describes how the second sentence functions in the text as a whole. The ﬁrst
sentence establishes something astronomers believe with some certainty: that Betelgeuse will explode in a supernova. The
second sentence then introduces a problem: astronomers aren’t certain when Betelgeuse will explode because they don’t
have enough information about the star’s internal characteristics. Finally, the third sentence indicates that researcher
Saraﬁna El-Badry Nance and colleagues investigated a possible method of obtaining the necessary information about
Betelgeuse’s internal characteristics, though they found that the method wouldn’t be suﬃcient. Thus, the function of the
second sentence is to identify the problem that Nance and colleagues attempted to solve but didn’t.
Choice A is incorrect because the second sentence introduces the general problem Nance and colleagues hoped to solve,
not a serious limitation of how Nance and colleagues tried to solve it. It is the third sentence that introduces Nance and
colleagues, but no serious limitation of their approach to studying a method of determining internal stellar states is
described. Choice B is incorrect because the second sentence introduces the general problem Nance and colleagues hoped
to solve, not the central ﬁnding they ultimately reported. It is the third sentence that presents Nance and colleagues’
conclusion that a potential method for determining internal stellar states would be insuﬃcient. Choice D is incorrect
because the second sentence doesn’t indicate how other astronomers or astrophysicists responded to the work done by
Nance and colleagues; the text doesn’t address this information at all.