#19 due to weathering and erosion the rock from the stream was smoothened and without as much the rock from deep underground was/is very rugged and natural.
#18 Due to wind patterns the sand dunes are blew around and the sands shift and fly around with nothing to keep the sand in place the sand can go long distances or come long distances.
Explanation:
When solid cadmium sulfide reacts with an aqueous solution of sulfuric acid then the reaction will be as follows.

Hence, ionic equation for this reaction is as follows.

Therefore, net ionic equation for this reaction is as follows.

D would be your best bet because evaporation occurs when water is heated, it then vibrates and then magic!
OMG WRONG THING SOOO SOO SORRYY i mean to put this answer on something else