The center of the earth is part of which earths sphere

Explanation: At the center of Earth is a solid inner core of nickel and iron. The Hydrosphere -- contains all the solid, liquid, and gaseous water of the planet. It ranges from 10 to 20 kilometers in thickness.

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smooth muscle is composed of involuntary muscles found within the walls of organs and structures such as the esophagus, stomach, intestines, and blood vessels. those muscles push materials like food or blood through organs. unlike skeletal muscle, smooth muscle can never be under your control.