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

Example Input: The nuclear envelope is a double-layered plasma membrane like the cell membrane, although without membrane proteins.
Example Output: The nuclear envelope is a double-layered plasma membrane like the cell membrane, although without what?

Example Input: Single-celled organisms and multicellular organisms have this in common: both have a way to get rid of waste materials.
Example Output: Which characteristic do single-celled organisms and multicellular organisms have in common?

Example Input: Water is an oxide of hydrogen.
Example Output:
Water is an oxide of what element?