Researchers studying magnetosensation have determined why some soil-dwelling roundworms in the Southern Hemisphere
move in the opposite direction of Earth’s magnetic ﬁeld when searching for ______ in the Northern Hemisphere, the magnetic
ﬁeld points down, into the ground, but in the Southern Hemisphere, it points up, toward the surface and away from worms’
food sources.
food:
food,
food while
food
Choice A is the best answer. The convention being tested is colon use within a sentence. A colon used in this way introduces
information that illustrates or explains information that has come before it. In this case, the colon introduces the following
explanation of why some roundworms in the Southern Hemisphere move in the opposite direction of Earth’s magnetic ﬁeld.
Choice B is incorrect because it results in a comma splice. A comma can’t be used in this way to join two long independent
clauses (“Researchers…food” and “in…sources”) such as these. Choice C is incorrect because it results in a run-on sentence.
The two clauses (“Researchers…food” and “in…sources”) are fused without punctuation. Furthermore, the conjunction “while”
fails to indicate that what follows is an explanation of why some roundworms in the Southern Hemisphere move in the
opposite direction of Earth’s magnetic ﬁeld. Choice D is incorrect because it results in a run-on sentence. The two clauses
(“Researchers…food” and “in…sources”) are fused without punctuation and/or a conjunction.