You are watching your favorite television program when a commercial for a new medication comes on. it states that the medication can alleviate depression: "since depression is a chemical imbalance, new effexor extended release can with mood, sleep, arousal, and alertness by working on the two key neurotransmitters involved in depression." these two neurotransmitters are:

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