According to the author (Plutarch), what caused the problem that led to the suggested reform by Tiberius Gracchus?

loess contribute to the flooding of rivers by providing the silt that is washed into rivers and constantly raises the bed of the rivers. this elevation above the surrounding flood plains and dams allow the river to overwhelm the dams and flood thousand of square miles of neighboring flood plains.

i got 3,4 and 5 as an answer