Answer the following question given this paragraph: 

Another benefit of Earth’s magnetic field is its use for navigation. People use compasses to detect Earth’s magnetic north pole and tell direction. Many animals have natural “compasses” that work just as well. For example, the loggerhead turtle in the Figure below senses the direction and strength of Earth’s magnetic field and uses it to navigate along migration routes. Many migratory bird species can also sense the magnetic field and use it for navigation. Recent research suggests that they may have structures in their eyes that let them see Earth’s magnetic field as a visual pattern. You can learn more at this URL: http://www. smithsonianmag. com/science-nature/How-Do-Birds-Find-Their-Way-Home. html.


Q: What part of earth do many animals use for navigation?

 Choices:

- oceans

- atmosphere

- molten core

- magnetic field

A:
magnetic field
