Which sentence is an example of chronological structure in "The City Without Us"?
 
A.
Unheated buildings would result in a destructive freeze-thaw cycle.
 
B.
Without daily pumping, Manhattan's subway tunnels would be flooded.
 
C.
After 20 years, rusted beams in buildings will cause them to start collapsing.
 
D.
If flooding were to go unchecked, steel support beams in buildings would rust.