Diaz conducts a decision-making experiment to determine if people reason more logically when they have more time to decide. All the participants who are under 40 are allowed 15 minutes to reach a decision about a problem; all the participants who are over 40 are allowed 20 minutes to reach a decision about the same problem. Diaz has a problem with his experimental design because

- the age of the participants is confounded with the independent variable.

Explanation:

In the given experimental design, the problematic area is that 'the participant's age is being disoriented with the independent variable.' The age of participants is creating an element of the puzzle in the experiment that will not only negatively affect the outcomes but it will lead to an unworthy/unreliable conclusion as well. Age in this experiment must not be considered as the aim is to test the impact of having extra time on the logical decision-making of the participants which may or may not vary across distinct age groups.

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.

i think it's b or c hope this