Reading Comprehension · Science
PrepTest 107 · Section 2 · Passage 3
Questions 16–21
Before you start
Open PrepTest 107, Section 2 in your official copy from LSAC and read the passage for Questions 16–21, using the structure guide below. The passage is not reprinted here.
Structure guide
- P1: opens with a long-known fact, states a newer conclusion and the clue that hinted at it, then lays out the first researcher's evidence and finding, adds a supporting study, and ends by naming a question that work left open
- P2: brings in a second researcher who answers the open question: an observation of behavior in stages, a hypothesis borrowed from a comparison, an experiment with an artificial trigger, a check against the real thing, and a broad generalization
Step 2 · The kid passage
How Bolt Finds Home in the Dark
For years, everyone in Ms. Rivera's class knew that the class robot, Bolt, had a front bumper full of tiny holes. Only this fall did the class decide that Bolt uses that bumper to find its charging pad when the lights go off, a guess hinted at by the fact that Bolt's camera shuts down in the dark. The proof came from Lulu's clipboard tests. Inside the holes she found two kinds of gadgets: push-buttons that feel a touch, and hum-catchers that pick up a faint buzz. Lulu saw that tapping one push-button lit up far more of Bolt's control screen than its camera or wheels ever did, so she decided the bumper is Bolt's main sense. A pencil poke backed her up: the signal raced down the blue wire to the brain chip, then on to the motor chip, and then (she guessed) Bolt lurched forward. But Lulu's tests never explained how Bolt finds the pad from across the room.
Priya cracked that part. First she watched: in the dark, Bolt rolls along swinging its bumper left and right. Near the pad, it switches to quick wiggly circles in one small spot, then rolls straight in and docks. Priya guessed Bolt listens for a hum, the way Grandpa's metal detector beeps near coins. So she hid a buzzing electric toothbrush on the floor. Bolt switched to wiggling, turned toward it from two floor tiles away (once from four), and tried to dock on it! Then Priya found that the real charging pad gives off the very same faint hum. She thinks every pad Bolt uses must hum.
Step 4 · The courtroom tale
The Case of the Sneaky Sprinkler
"Your Honor, my client's lawn sprinkler did not soak the mail carrier on purpose," said Mr. Whitfield, snapping his suspenders. "It sprays whatever moves." First he showed a video: the idle sprinkler slowly swiveled left, then right, then left. Next he rolled a beach ball across the grass. The sprinkler stopped swiveling, twitched in short jerky bursts, locked on, and drenched the ball. "No mail carrier required," he said. Then he played a second clip. The neighbor's cat strolled past and got the exact same soaking. "The gadget hunts motion. My best guess is that anything moving on that lawn gets sprayed." Judge Okafor dabbed her damp sleeve. "Noted, Counselor. Next time, keep the demonstrations outdoors."