Hello I need help with this

What does the word submerged mean in the following sentence? after it rained for three days in a row, the streets were completely submerged.

The lines marked by the letters a, b, and c on the map above represent a. chains of volcanoes b. earthquake fault lines c. thin strips of heavy forests d. major rivers that flow from north to south

Why slip off slopes are found on the inside of meanders? why river cliffs are found on the outside of meanders?