The answer is allusion.
Allusion is mentioning something briefly, not really going into the details of it.
Pollution could be a focus you could write about.
Memoirs and autobiographies (option "C") are examples of nonfiction literature, since the writer reports on his / her real life events by making use of different literary techniques. Literary nonfiction, also known as creative nonfiction, employs literary elements, like character, setting and plot. The employment of literary styles and techniques in nonfiction narratives are intended to entertain the reader by creating factual narratives about people, places, and events of the real world.
