Question

read the passage.
making towers bird - friendly
the lights on tall communication towers warn pilots to avoid the towers when flying at night. unfortunately, the steady red lights often used on towers have the opposite effect on birds: the bright beams attract and confuse them. instead of avoiding the lights, the birds fly directly toward them, crashing into the towers or becoming entangled in power lines. millions of birds have died this way. however, there is a solution. unlike steady lights, flashing or blinking lights dont attract birds. in response to demands from conservation groups, the federal aviation administration in 2016 began requiring communication towers in the u.s. to use blinking lights instead of steady ones.
what is the main, or central, idea of the passage?
birds are attracted to the steady red lights on communication towers.
to save birds, communication towers have begun using blinking lights.

Explanation:

The passage first describes the problem of steady - red lights on communication towers attracting and harming birds. Then it presents the solution: communication towers have started using blinking lights instead of steady ones to save birds. The first option only mentions the problem (birds being attracted to steady lights), while the second option includes both the problem (implied as the reason for the change) and the solution (using blinking lights to save birds), which is more comprehensive as a central idea.

Answer:

To save birds, communication towers have begun using blinking lights.