Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Plasma membranes encloses and defines the borders of cells.
What encloses and defines the borders of cells?

Most of the digestion reactions occur in the small intestine.
Where do most of the digestion reactions occur?

Squamous cell carcinoma is the second most common skin cancer.

What is the second most common skin cancer?