Final answer:
Option B is correct because it uses commas to correctly separate the year range from the rest of the sentence.
Step-by-step explanation:
The correct way to punctuate the sentence about the artist's productive period is with commas to set off the year range. Therefore, option B, "The artist's urban period, 1947-1956, was one of his most productive times," is the grammatically correct choice. Commas are used here to separate the parenthetical element (the years) from the rest of the sentence, which is a common punctuation convention in English grammar.