The pile-up of sand and silt at the site where a river flows into the ocean forms a

As a river flows, it picks up sediment from the river bed, eroding banks, and debris on the water. The river mouth is where much of this gravel, sand, silt, and clay—called alluvium—is deposited. When large amounts of alluvium are deposited at the mouth of a river, a delta is formed.

Explanation:

As a river flows, it picks up sediment from the river bed, eroding banks, and debris on the water.

Explanation:

c. heat could easily travel through the molecules in the air and escape/enter the flask. removing the air slows down the heat transfer.  

i think it's c. if you look search electronic symbol on google and then click on wiki it shows you a