Final answer:
The sentence with an analogy is sentence number 2, which compares the armadillo's protective shell to the armor of medieval knights, helping readers understand the protective function of the shell.
Step-by-step explanation:
The sentence that contains an analogy is sentence number 2: "Like knights of medieval times, armadillos have their own armor, a thick, tough shell to protect them from their enemies." An analogy is a comparison that shows how two different things are similar in some ways, often used to help explain something unfamiliar in terms of something familiar. In this case, the analogy helps the reader understand the function of an armadillo’s shell by comparing it to the armor worn by knights, which is more familiar to most people. This makes it easier to grasp the concept that an armadillo's shell serves as a protective barrier against threats, just as a knight's armor does.