Its correct letter.
a. an area that shares common features
Is it natural features

i would expect light rain in pittsburgh throughout the following 24 to 48 hours. the lower/falling weights in urban areas toward the west demonstrate that a low weight framework is moving from west to east toward pittsburgh. low weight frameworks are ordinarily connected with precipitation. the way that you don't see a major drop in temperature in the more western urban areas demonstrates the low weight framework is moving with a warm front, so just light rain would be normal. substantial downpours or progressively vicious climate is just typically connected with chilly fronts, where the warm air is pushed up and over a cool front quickly. this quickly rising air (convection) is what gives you heavier torrential downpours, and other conceivably serious weather conditions.

question

which are human systems?

the amazon rain forest

the appalachian trail

the george washington bridge

the himalayas

the hoover dam

the north american free trade agreement