Question

read the passage.
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 h
n searchers cant or shouldnt.
cockroach - like robots can fit through small cracks and move through unstable rubble.

Explanation:

The passage first mentions the danger of human rescue workers in collapsed buildings. Then it introduces real cockroaches' features (strong yet flexible exoskeletons, ability to flatten bodies). After that, it says researchers were inspired to create roach - robots. And finally, it mentions the roach - robots' functions (squeeze through small spaces, skitter over unstable environments, used with cameras and microphones to locate victims). The main idea should cover the problem (danger for human rescuers), the inspiration (cockroaches), and the solution (roach - robots). The second option "It is dangerous to search inside collapsed buildings, but cockroach - like robots can go places where human searchers can't or shouldn't" best combines these elements. The first option only focuses on the inspiration and creation, not the problem - solution aspect. The third option only focuses on the robots' features, not the overall context of why they were created.

Answer:

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