Which of the following was the greatest issue leading to the monroe doctrine?
1the united states was concerned about renewed european colonization efforts in the wake of latin american independence movements.
2the united states feared retaliation from spain, as the latter was bitter over the louisiana purchase from france, who had only recently regained the territory.
3the united states recognized that diplomacy was the best method to acquire new territory and wanted to assure europe of its intentions to continue peaceful relations.
4the united states had gained significant property in recent years, was having trouble establishing control in those areas, and needed justification for expanding the federal military.

the underground railroad (apocope of the metropolitan railroad) is a system of urban trains located within a city and its metropolitan area. it is characterized for being a massive transport of passengers in the big cities, uniting diverse zones and their environs, with high capacity and frequency and in segregated form to other systems of transport. metropolitan railroads are built underground or on the surface, although most systems use mixed models where sections are combined in both modalities.

1 - as a result, the metro tends to reduce car travel for two reasons: first, due to the greater transfer of users from the car and, second, due to the reduction in the acquisition of cars in homes located in sectors near the stations of the metro.

2 -the metro allows to contribute effectively to the achievement of all the objectives of an urban development policy: it improves the efficiency of the city's economy by reducing travel costs and also generates a higher level of activities in the city center, taking advantage of of the agglomeration economies.

3 -it is a clean means of transport, since it uses renewable energy (usually electricity), taking care of the environment and avoiding excessive pollution.