Answer: a. decreases the present and future risk to human properties
Step-by-step explanation:
Properties along the coasts can be in danger when high tides come in. This can however be mitigated by walls protecting those properties as it would take a significantly high tide (flood proportion) to scale those walls and come in and damage the property.
These walls therefore not only decrease the present risk to human properties but if maintained, decrease the future risks as well.