A study published by Rice University geoscientist Ming Tang in 2019 offers a new explanation for the origin of Earth’s ______
structures called arcs, towering ridges that form when a dense oceanic plate subducts under a less dense continental plate,
melts in the mantle below, and then rises and bursts through the continental crust above.
continents geological
continents: geological
continents; geological
continents. Geological
Choice B is the best answer. The convention being tested is punctuation use between a main clause and a supplementary
phrase. In this choice, a colon is correctly used to mark the boundary between the main clause (“A study…continents”) and
the supplementary phrase (“geological…above”) and to introduce the following explanation of the origin of Earth’s continents.
Choice A is incorrect because it fails to mark the boundary between the main clause (“A study…continents”) and the
supplementary phrase (“geological…above”) with appropriate punctuation. Choice C is incorrect because a semicolon can’t
be used in this way to join the main clause (“A study…continents”) and the supplementary phrase (“geological…above”). A
semicolon is conventionally used to join two main clauses, whereas a colon is conventionally used to introduce an element
that explains or ampliﬁes the information in the preceding clause, making it the better choice in this context. Choice D is
incorrect because it results in a rhetorically unacceptable sentence fragment beginning with “geological.”