Alittle boy is allowed to play with a laboratory rat and shows no fear of it. then, a scientist makes a scary noise by banging an iron bar whenever the little boy reaches for the rat. soon, the boy begins crying whenever the rat comes near him. in this study, the scary noise is the

gold discovery in california, and pioneer settlers were sometimes pulled west because they wanted to make a better living. others received letters from friends or family members who had moved west. these letters often told about a good life on the frontier. the biggest factor that pulled pioneers west was the opportunity to buy land.

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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