The diagram below shows the branching tree diagram for cats.

A slanting, horizontal line is shown. On the extreme left, there is a label that says Common Ancestor. Along the slanting, horizontal line there are five dots labeled from left to right with the following traits, Four limbs, Amniotic egg, Fur, Shearing teeth, and Retractable claws. There is one vertical line between each of the consecutive five dots. The lines are labeled from the from left to right as Amphibians, Reptiles, Marsupials, Dogs, Cats.

Which characteristic is shared by the least number of organisms? (5 points)

a
Amniotic egg

b
Four limbs

c
Shearing teeth

d
Retractable claws