Explanation
Correct answer: B.
Choice B is the best answer. The convention being tested is the punctuation of elements in a complex series. It’s conventional to use a semicolon to separate items in a complex series with internal punctuation, and in this choice, the semicolon after "time" is conventionally used to separate the first item ("offered…time") and the second ("celebrated…holiday") in the series of activities that librarian Pura Belpré offered. Moreover, the semicolon after "time" matches the semicolon used later to separate the second item ("celebrated...holiday") and the third ("and...folktales") in the series.
Why the other choices are wrong
Choice A
Choice A is incorrect because it fails to use appropriate punctuation to separate the first item and the second item in the complex series. Furthermore, a comma isn’t needed between the noun "practice" and the prepositional phrase "at the time" because the prepositional phrase is essential to the full meaning of the phrase "an uncommon practice at the time."
Choice C
Choice C is incorrect because a comma after "time" doesn’t match the semicolon used later to separate the second ("celebrated...holiday") and third ("and...folktales") items in the series. Furthermore, a comma isn’t needed between the noun "practice" and the prepositional phrase "at the time" because the prepositional phrase is essential to the full meaning of the phrase "an uncommon practice at the time."
Choice D
Choice D is incorrect because a comma after "time" doesn’t match the semicolon used later to separate the second ("celebrated...holiday") and third ("and...folktales") items in the series.