Question

roach robots to the rescue
when buildings collapse, it is extremely difficult to safely locate and rescue people trapped inside. victims may be wedged into small spaces, and unstable rubble could collapse on rescue workers. an alternative to human rescue workers may be robotic cockroaches. real cockroaches are protected by strong yet flexible exoskeletons. they can also flatten their bodies through tiny cracks. a robotics researcher from harvard university and a biomechanics expert from the university of california, berkeley, were inspired to create mini robots that have the same features. the roach robots can squeeze through small spaces and skitter over unstable environments. fitted with cameras and microphones, they could be used in disasters to locate victims.
what is the main, or central, idea of the passage?
inspired by the strength and quickness of cockroaches, researchers created robots with the same characteristics.
it is dangerous to search inside collapsed buildings, but cockroach - like robots can go places where human searchers cant or shouldnt.
cockroach - like robots can fit through small cracks and move through unstable rubble.

Explanation:

The passage first introduces the danger and difficulty of human rescue in collapsed buildings, then explains that researchers created roach robots inspired by real cockroaches' features (strong yet flexible exoskeletons, flattening bodies) to solve this problem—these robots can access spaces human rescuers can't or shouldn't. The first option only mentions creation inspiration without the rescue context; the third option only describes the robots' abilities without the purpose. The second option connects the problem (danger of human search) and the solution (cockroach-like robots accessing inaccessible places), which covers the passage's core idea.

Answer:

It is dangerous to search inside collapsed buildings, but cockroach-like robots can go places where human searchers can't or shouldn't.