Find the odd pair.

Let's analyze the relationship shared by the pairs across the options:
* Dog : Puppy $\to$ A Puppy is the offspring (young one) of a Dog.
* Cow : Calf $\to$ A Calf is the offspring (young one) of a Cow.
* Sheep : Lamb $\to$ A Lamb is the offspring (young one) of a Sheep.
* Tortoise : Turtle $\to$ Tortoise and Turtle are two distinct types of reptiles belonging to the same order, not a parent-offspring pair.

Since Option C does not represent a parent-offspring relationship, it is the odd pair.