The correct answer is C. Rivers wash away salts from earth and pour them into the sea.
Sea water is saltier than rain water because it contains dissolved salts from the rocks and minerals that it flows over. These salts are carried into the sea by rivers and streams, and they accumulate over time. The average salinity of sea water is about 35 parts per thousand, while the average salinity of rain water is about 0.05 parts per thousand.
Option A is incorrect because sea animals do not produce salt. Option B is incorrect because the air around the sea is not saltish. Option D is incorrect because sea beds do not have salt producing mines.