Colliding tectonic plates

This task is about earthquakes and tectonic plates.
Colliding tectonic plates
The diagram shows two of the plates that make up the Earth's surface colliding with each other. In this collision one plate is going under the other plate. Some of the associated geological features with this have been drawn in the diagram.
Explain why the following geological features or events have occurred.

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a)  Why are earthquakes occurring in this area?

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b)  How did the mid-ocean ridge form?

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c)  Why is an ocean trench present?

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d)  Why do volcanoes occur in this area?