Aspecies can develop genetic diversity.
a. immediately
b. over a short period of time
c. over a long period of time
d. over any period of time

The correct answer is-  C. over a long period of time.

Genetic diversity can be described as the sum of all the genetic characteristics, which correspond to the genetic makeup of all the organisms within a species.

Genetic diversity allows the organisms of a population to adapt to the changing environmental conditions as beneficial alleles allows the differential survival and reproduction of an organism.

Thus, a species  develop genetic diversity over a long period of time that brings desirable modification or lead to the evolution of new species.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.