What do we call the phenomenon of the rhythmic rising and falling of ocean water twice a day?

Consider statements A and B about Tsunami waves and choose the correct answer: (A) Volcanic eruptions can never lead to the formation of Tsunami waves. (B) The first indication of an approaching Tsunami is the rapid withdrawal of water from the coastal region, followed by a destructive wave.

Consider the statements (A) and (B) on high tides and choose the correct option: (A) They raise the water level close to shores, which helps the ships to arrive at the harbour. (B) They create problems for fishermen as fishes move away from the shore during high tide.