Questions: Under which condition below would you expect a coarse-grained intrusive rock like diorite to form? A. Lava slowly flowing out of a fracture in Earth's surface B. Quick cooling below Earth's surface C. Slow cooling in the upper mantle D. Within a zone of fractured rocks below Earth's surface

The answer is C: Slow cooling in the upper mantle.

Explanation for each option: A. Lava slowly flowing out of a fracture in Earth's surface - This would result in an extrusive rock, not an intrusive one. Extrusive rocks cool quickly on the surface and are typically fine-grained. B. Quick cooling below Earth's surface - Quick cooling would result in fine-grained rocks, not coarse-grained ones. C. Slow cooling in the upper mantle - Slow cooling allows large crystals to form, resulting in a coarse-grained texture typical of intrusive rocks like diorite. D. Within a zone of fractured rocks below Earth's surface - This condition does not necessarily imply slow cooling, which is required for the formation of coarse-grained intrusive rocks.

Summary: Coarse-grained intrusive rocks like diorite form under conditions of slow cooling, which allows large crystals to develop. Therefore, the correct answer is C: Slow cooling in the upper mantle.