The name of the volcano is SANTORINI.
Santorini is an island in Greece and this name is used to called the volcano which occurred there. Santorini is an a dormant and active volcano; its last eruption was in 1950. The volcano of Santorini is a very famous volcano in Greece and it has the highest crater in the world.
Answer:
use bigger dams,
the underground system clear
make sponge city
I think it is the 3rd answer choice.
It means to guess/round a number.