For numbers 1-5, use the following choices as described below:
A. Cytoskeleton B. Rough ER
C. Golgi apparatus D. vacuole
E. ribosome

______1. It is the site of protein synthesis.
______2. It stores water, ions, and other substances needed by the cell.
______3. It contains ribosomes.
______4. It sorts, packages and modifies proteins produced in the ER.
______5. It serves as the backbone of the cell.
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