Question

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.
cockroach - like robots can fit through small cracks and move through unstable rubble.
it is dangerous to search inside collapsed buildings, but cockroach - like robots can go places where human searchers cant or shouldnt.

Explanation:

The passage introduces cockroach - like robots. It first points out the difficulty of rescuing people in collapsed buildings. Then it mentions that researchers were inspired by cockroaches to create these robots, and these robots can be used in disasters to locate victims. The first option "Inspired by the strength and quickness of cockroaches, researchers created robots with the same characteristics." is too narrow as it only focuses on the creation inspiration. The second option "Cockroach - like robots can fit through small cracks and move through unstable rubble." only describes the robot's ability. The third option "It is dangerous to search inside collapsed buildings, but cockroach - like robots can go places where human searchers can't or shouldn't." comprehensively covers the problem of rescue in collapsed buildings, the danger of human search, and the advantage of cockroach - like robots in such situations, which is the main 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.