Final answer:
The Earth's outer core is the only layer that is in a liquid state.
Step-by-step explanation:
The correct answer is OB. Outer core. The Earth's layers are divided into the crust, mantle, and core. The outer core is the only layer that exists in a liquid state. It is composed mostly of molten iron and nickel, and its movement generates the Earth's magnetic field.
Learn more about Earth's layers