The answer is D, or it is the answer most commonly held. The more you read, the more different words you will come across, unless you are reading nothing but comic books and even they have the word you won't find everywhere.
Usually words are embedded in something that will suggest their meaning. You may get the wrong meaning, but usually you get the meaning close enough.
One possible theme could be “how a person is affected by growing older”. Shakespeare compares old age to the seasonal shift. The narrator also describes how aging is harsh and ultimately comes to see its inevitability. Hope this helps!
