Question

saving sea turtles
small - scale fishing performed with nets is one of the most common fishing methods used around the world. one of the unfortunate side effects of this method is that sea turtles, which are considered threatened, get caught in the nets along with the fish. conservation biologists at the university of exeter in england recently devised a way to prevent these sea turtle deaths, which they tested at a fishery in northern peru. they found that attaching green led lights to the nets warned the turtles away, possibly because the lights made the nets more visible. the number of sea turtle deaths was reduced, but the number of fish caught seemed to remain the same.
what is the main, or central, idea of the passage?
to prevent turtles from becoming caught in fishing nets, conservation biologists attached led lights to the nets.
conservation biologists are researching ways to save the threatened sea turtle population.
one problem with small - catch fishing is that sea turtles get caught along with fish.

Explanation:

The passage starts by introducing a problem (sea turtles getting caught in fishing nets) and then presents a solution (conservation biologists attaching green LED lights to the nets). The other options are either just parts of the overall story (like the problem - sea turtles getting caught or the fact that conservation biologists are researching) rather than the main idea which encompasses the problem - solution aspect.

Answer:

To prevent turtles from becoming caught in fishing nets, conservation biologists attached LED lights to the nets.