Given a scientific question, generate a correct answer to it.

Example Input: A black solid by itself, this element is incredibly important because of what it makes when it combines with many other elements, including oxygen?
Example Output: carbon

Example Input: Organelles whose membranes are specialized for aerobic respiration are called what?
Example Output: mitochondria

Example Input: The epidermis is made of which closely packed cells?
Example Output:
epithelial cells