Explanation
Correct answer: B.
Choice B is the best answer. The phrase “according to Swentzell” is an aside that interrupts the flow of the sentence, so it needs to be separated from the sentence with a pair of matching punctuation marks: two commas, two dashes, or a pair of parentheses. We already have a comma before “according,” so we must add a comma after “Swentzell.” .
Why the other choices are wrong
Choice A
Choice A is incorrect. This choice creates a punctuation error. The phrase “according to Swentzell” is an aside that interrupts the flow of the sentence, so it needs to be separated from the sentence with a pair of matching punctuation marks: one before and one after the phrase.
Choice C
Choice C is incorrect. This choice creates a punctuation error. “The arrangement of the figures, according to Swentzell” is not an independent clause, so it can’t come before a colon.
Choice D
Choice D is incorrect. This choice creates a punctuation error. The phrase “according to Swentzell” is an aside that interrupts the flow of the sentence, so it needs to be separated from the sentence with a pair of matching punctuation marks. We already have a comma at the beginning, so we have to use another comma here to match. We can’t just switch to a dash! .