echolocation is when some animals detect objects by hearing echoes by emitting sound
A pod of dolphins is swimming while searching for food. The youngest dolphin swims away from the pod and is lost. The rest of the pod searches for the young dolphin by clicking into the water. The young dolphin is found because of

Select from the following.
(I) echoes from noise
(II) vibrations from drums
(III) sound of water
(IV) movement in air
(I)