Help me with this please​

C. Protective Barrier against infection and disease

Explanation:

The skin does not send chemical messages, nor electrical, and the skeletal and muscular system is what allows movement and structure, which leaves C as the answer because it is what protects outside diseases from getting into your blood or arteries

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a time line cause it goes from 685 to 978

explanation:

on disadvantage of hydroelectric power is the cost. another disadvantage of using hydroelectric power is finding a water source powerful enough to harvest hydroelectric power.