The correct answer is option 'D': All of the above.

Earthquakes are a natural phenomenon that occurs when there is a sudden release of energy in the Earth's crust, causing the ground to shake. They are most prone to occur in areas where certain geological conditions exist. Let's examine each option to understand why they are all correct:

1. Active Volcanoes:
- Volcanic activity often occurs in areas where tectonic plates meet, resulting in the formation of active volcanoes. These areas are known as volcanic zones or volcanic arcs.
- Volcanic eruptions are associated with the movement of magma from beneath the Earth's surface. As the magma rises, it can cause the surrounding rocks to fracture and create pathways for seismic waves to propagate, leading to earthquakes.
- Additionally, the pressure exerted by the magma can cause the Earth's crust to deform, resulting in stress accumulation and subsequent release in the form of earthquakes.

2. Large Reservoirs:
- Large reservoirs, such as those created by the construction of dams, can also trigger earthquakes. This phenomenon is known as reservoir-induced seismicity.
- When a reservoir is filled with water, the weight of the water puts additional stress on the underlying rocks and increases the pore pressure within them. This can destabilize the rocks and trigger seismic activity.
- The increased pore pressure can reduce the effective stress between rock grains, making them more susceptible to sliding along pre-existing fault planes and generating earthquakes.

3. Tectonic Fault Planes:
- Tectonic fault planes are areas where two tectonic plates meet and interact. These interactions can result in the accumulation of stress along the fault lines.
- When the stress exceeds the strength of the rocks, it can cause them to fracture and slip, resulting in an earthquake. The release of accumulated stress along fault planes is the most common cause of earthquakes worldwide.
- Some well-known examples of tectonic fault planes include the San Andreas Fault in California and the Himalayan Frontal Thrust in the Himalayas.

In conclusion, earthquakes are most prone to occur in areas where there are active volcanoes, large reservoirs, and tectonic fault planes. These geological conditions contribute to the build-up and release of stress within the Earth's crust, leading to seismic activity. Therefore, the correct answer is option 'D': All of the above.