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Answer:
Troponin and calcium ions.
Explanation:
Troponin is a component of thin filament along with tropomyosin and actin. It is a protein complex to which calcium binds and start the production of muscular force.
Calcium also playing a very important role in muscle contractions, it binds with troponin and helping to move tropomyosin.
When calcium ion attached to troponin, then conformational changes occurs in troponin shape and moves which allow tropomyosin going away from its inhibitory position from the myosin-binding sites on actin. After this, the energized myosin head starts binding to the actin molecules and starts the cross bridge cycle, which helping in shortening the muscle's fiber.
The Grand Canyon is a Canyon that exist where an ancient river once flowed. The hydrosphere (all of water on earths surface.) Slowly eroded away at the rock of the grand canyon until a Canyon was formed this water evaporated into the atmosphere then percerpertated back down creating a cycle that ended with the formation of the grand canyon.