You want to know whether chewing gum will cause someone to perform better on tests. When designing the experiment, which of the following best describes your control group? Select one:
a. A group of individuals that chew two pieces of gum.
b. A group of individuals not chewing gum.
c. A group of individuals that sucked on hard candy.
d. A group of individuals that chew a half a piece of gum.

What feature of cell theory is best demonstrated in the image

15 ! come and answer! a(n) is the general term for an infectious disease that has spread across a city, region, or country.

To answer this question, researchers studied populations of the dusky salamander (desmognathus ochrophaeus) living on different mountain ranges in the southern appalachian mountains. the researchers tested the reproductive isolation of pairs of salamander populations by leaving one male and one female together and later checking the females for the presence of sperm. four mating combinations were tested for each pair of populations (a and b)—two within the same population (female a with male a and female b with male b) and two between populations (female a with male b and female b with male a). the proportion of successful matings for each mating combination was measured. for example, when all the matings of a particular combination were successful, the researchers gave it a value of 1; when none of the matings were successful, they gave it a value of 0. then the researchers calculated an index of reproductive isolation that ranged from 0 (no isolation) to 2 (full isolation). the reproductive isolation value for two populations is the sum of the proportion of successful matings of each type within populations (aa + bb) minus the sum of the proportion of successful matings of each type between populations (ab + ba). the table provides data for the geographic distances and reproductive isolation values for 27 pairs of dusky salamander populations.