To make it more interesting for your audience and form credibility
the answer is: C. After 20 years, rusted beams in buildings will cause them to start collapsing.
Chronological structure refers to a technique that put events in proper sequence starting on the earliest time to the latest. The phrase 'after 20 years' indicate the author first explain the situation before the 20 years process occurs and continue in proper sequence to explain what happen next.
The mode of persuasion "ethos" appeals to beliefs or ideals of a community and also an authority figure's character or credibility to influence individuals through morals.
In the famous play "Julius Caesar", Mark Anthony changed the opinion of the Romans by making them hate Brutus and the conspirators using "ethos" to put their credibility on the spot with irony and sarcasm when he repeatedly calls them "Honorable Men"; on the other hand he praise Caesar's loyalty to him when he calls him "His faithful friend", making people empathize with his character.
Is this the excerpt you are referring to?
<span>In a smithy
one sees a white-hot axehead or an adze
plunged and wrung in a cold tub, screeching steam-
the way they make soft iron hale and hard—:
just so that eyeball hissed around the spike.
</span>
If so, the use of the epic simile in this excerpt helps the reader understand how hot the spear actually is.
