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: Wave amplitude and wavelength are two important measures of wave size.
Example Output: Wave amplitude and wavelength are two important measures of what?

Example Input: Laca is the third gene of lac operon in addition to lacz and lacy.
Example Output:
What is the third gene of lac operon in addition to lacz and lacy?