Use the two maps below to answer the following question:

on the top, a map shows major trade routes from china, through the himalayas, to the west. on this map, samarkand lies just southeast of the aral sea in persia and bukhara lies just to the west of samarkand. on the bottom, a map shows the major geographic features of india, china, middle east, including rivers and altitude. this map shows elevation with green indicating the lowest elevation, yellow the next highest elevation, and orange the highest elevation. the areas shaded orange are the western part of the arabian peninsula, persia, western and northern china. areas shaded yellow are the central arabian peninsula, far northern persia, far northern and some coastal areas of china, and southwestern india. all other areas are shaded green.

which of these describes why samarkand and bukhara were important trade centers on the silk road?

they were high-altitude cities in passes in the mountains.
they were low-altitude cities in the fertile plain of the indus river.
they were low-altitude cities in valleys that cut through mountains.
they were high-altitude cities in the fertile plain of the indus river