Tissues combined to form . a. organs
b. an organism
c. cells
d. an organ system

Your answer is A. Organs

Explanation:

molecules combine to form cells, cells combine to form tissues, tissues combine to form organs, organs combine to form organ systems, and organ systems combine to form organisms.

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every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.