the world's current population is 7.3 billion and the world population in 1915 was 1.8 billion. The increase over the past century is 7.3 billion - 1.8 billion = 5.5 billion. So, the correct answer would be "more than 5 billion" (option D).
Europe is sometimes called a "peninsula of peninsulas", to draw attention to the fact that Europe is a relatively small, elongated appendage to Asia, and that a large part of Europe is made up of peninsulas.
