Deep trenches in the ocean mark places where A) one plate slides under another, returning older crust to the mantle. B) plates pull apart, leaving great rifts in the crust. C) hot mantle material rises upward and spreads sideways, pushing the plates apart. D) plates push together, creating ocean mountain chains. E) plates slip sideways relative to one another.

Option (A)

Explanation:

Trenches are usually defined as deep and narrow depressions that are formed along the convergent plate boundaries. These are the region where two tectonic plates move towards each other and result in the formation of a subduction zone, where the denser plate subducts below the less dense one. As the heavier plate goes down, it reaches the mantle and the rocks undergo partial melting.

These trenches are located just above this zone of subduction. It can also be said that the presence of a trench indicates a subduction zone.

One of the famous trenches is the Mariana trench which is present in the Pacific ocean and it has a depth of approximately 11 km from the mean sea level.

Thus, the correct answer is option (A).