The correct answer is: b) Erosion.
Seawalls are a type of coastal protection structure that is constructed to protect the shoreline from erosion. They are typically made of concrete or stone, and they are built parallel to the shoreline. Seawalls can be effective in preventing erosion, but they can also have negative environmental impacts. For example, they can disrupt the natural flow of sand along the shoreline, and they can also create a barrier between the land and the ocean.
Tidal waves, also known as tsunamis, are large waves that are caused by earthquakes or volcanic eruptions. They can travel at speeds of up to 800 kilometers per hour, and they can cause extensive damage when they hit land. Seawalls are not effective in protecting against tidal waves, as the waves are simply too powerful.
Earthquakes are caused by the sudden movement of tectonic plates. They can cause significant damage to coastal infrastructure, including seawalls. However, seawalls are not designed to protect against earthquakes, and they are unlikely to be effective in doing so.
Floods are caused by an excessive amount of water that inundates an area. They can be caused by heavy rains, snowmelt, or dam failures. Seawalls can be effective in protecting against floods, but they are only effective if they are built to the appropriate height.