Hydrothermal vents are common features found in the deep ocean. They are associated with various geological processes and occur in specific regions. The correct answer to the given question is option 'D', which states that hydrothermal vents are closely associated with all of the following:

a) Mid-oceanic ridges:
- Mid-oceanic ridges are underwater mountain ranges that run through the center of the ocean basins. They are formed by the divergence of tectonic plates, where new oceanic crust is created as magma rises and solidifies.
- Hydrothermal vents are commonly found along mid-oceanic ridges. This is because the tectonic activity at these ridges allows for the release of heat and the formation of cracks in the ocean crust, through which hydrothermal fluids can escape.

b) Intersection of continental plates:
- Continental plates are large pieces of the Earth's lithosphere that make up the continents. When these plates interact at their boundaries, they can form various geological features such as mountains, volcanoes, and trenches.
- In some cases, the interaction between continental plates can lead to the formation of hydrothermal vents. This can occur when one plate sinks beneath another in a process known as subduction. As the subducting plate descends into the mantle, it heats up and releases fluids that can rise back to the surface and form hydrothermal vents.

c) Areas of seafloor spreading:
- Seafloor spreading is the process by which new oceanic crust is formed at mid-oceanic ridges and spreads outward. It occurs due to the divergence of tectonic plates, where magma rises and solidifies to form new crust.
- Hydrothermal vents are closely associated with areas of seafloor spreading because the heat and cracks generated during this process provide ideal conditions for the formation of hydrothermal systems. The rising magma heats the surrounding water, which then circulates through the fractures and carries minerals from the crust. As the heated fluids rise to the surface, they mix with the cold seawater, resulting in the formation of hydrothermal vents.

In conclusion, hydrothermal vents are closely associated with mid-oceanic ridges, the intersection of continental plates, and areas of seafloor spreading. These geological processes provide the necessary conditions for the formation of hydrothermal systems, where hot fluids and minerals are released into the ocean.