A researcher has observed that children who eat more sugar tend to show a higher level of activity than children who eat less sugar. However, the researcher suspects that the apparent relationship may be explained by the fact that some children have a higher rate of metabolism, which causes them to eat more and to be more active compared to children with a lower rate of metabolism who eat less and are less active. This is an example of the .

The correct answer is the third variable problem

A system of equations can be formed by several unknowns, but it will only be solved if the number of unknown terms is equal to the number of equations in the system. The systems with three variables can be solved through the processes already known and studied, substitution or addition.

first, the romans stayed isolated because they had to defend their own territories from neighboring cities that were harassing them, like the etruscans. second, once the romans managed to defeat their neighbors, and started to expand their territory, they started to build roads and bridges. finally, now that the romans have covered their territory with roads functioning as highways, they could mobilize their legions faster to assemble larger military units in a specific place.

according to classical republican political theory, which democratic republics would function best?

a.   small republics, with people who had similar interests

b.   large republics, with people who had competing interests

c.   republics made up entirely of landowners

d.   republics made up entirely of servants