The correct answer is: I, II, and III.
Tsunamis can be caused by:
I. Earthquakes - Most commonly, tsunamis are triggered by undersea earthquakes. II. Volcanic eruptions - Volcanic activity, including explosive eruptions and the collapse of volcanic structures, can generate tsunamis. III. Landslides - Underwater landslides or landslides that enter the water can also displace enough water to produce a tsunami.
Therefore, all three factors can cause tsunamis.