Variation in a new generation of organisms is the result of
a. sexual reproduction involving one parent
b. sexual reproduction involving two parents
c. asexual reproduction involving one parent
d. asexual reproduction involving two parents

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.

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.