By about 1700 b. c.e., the residents of harappa and mohenjo-daro began to abandon their cities because
a) frequent epidemics made city living impossible.
b) deforestation of the indus river valley brought about ecological degradation.
c) the horse-riding aryans began to invade the cities.
d) the indus river dried up.
e) all these answers are correct.

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.

pope john paul ii ( his real name is karol wojtyla) and lech walesa ( the leader of the solidarity movement ) were both born in poland.