Assertion (A): Birds avoid migrating to places where noise level is above 100 dB.

Reason (R): Doctors and scientists have now medically confirmed that noise disturbs living organisms.

1. Both A and R are true and R is the correct explanation of A.
2. Both A and R are true but R does not explain A.
3. A is true but R is false.
4. A is false but R is true.

Both A and R are true and R is the correct explanation of A.

Explanation — Birds rely heavily on sound for communication, navigation, and detecting predators. That's why birds avoid migrating to places where noise level is above 100 dB. Some of the birds have been found to have stopped laying eggs due to noise pollution. Hence, doctors' and scientists' confirmation that noise (in excess of about 100 dB) disturbs living organisms and their respective functions explains why birds avoid such areas.