Answer:
The correct choice is B) When Shakespeare was a boy, he never dreamed he would become a world-famous playwright.
In this sentence, the phrase "When Shakespeare was a boy" is an introductory phrase that provides additional information about the timing of the action. It is separated from the main clause, "he never dreamed he would become a world-famous playwright," by a comma. This comma is necessary to indicate a pause and to clarify the structure of the sentence. The correct punctuation helps to improve readability and understanding.