Explanation: The answer is A because the the 2 actions are related. It is not B because the sentence is incompletely transitioned, without a proper transition word. It is not C because you do not start a new sentence with a transition word and finally it is not D because Without the previous sentence it does not tell you what they missed.
Subheadings give the reader an idea of what will be discussed in the section. For example, 'How Did WWII Shape Daily Life?' This subheading shows the reader that it will be about how WWII changed the daily lives of people. By the end of the section, the reader should have a firm answer to the question.