Which organism has the least visible postanal tail as an adult?
a. crow
b. fish
c. lizard
d. human
e. dog

Option 'D' is correct.

Explanation:

Human has least visible postanal tail as an adult.

Whereas fish, lizard, crow and dog has developed visible postanal tail.

Human too have tails but it does not developed as much as to be visible after infancy.

Hence, option 'D' is correct.

the reason the two sea urchins don't compete with each other for food, resources, etc. is because the urchins have adapted to the environment but they have also adapted to each other. this is most likely because the genes of the sea urchins.