Answer:
Option B. They use thermal updrafts to stay aloft
Step-by-step explanation:
The sunlight warms the surface of the earth during noon and morning time and when this warming of the Earth's surface is not evenly done or uniform then this gives rise to the thermals. These are the rising air columns and rises when the air nearest to the earth heats up.
This is how some birds like vultures make use of the thermal updrafts to maintain flight.