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

Q: Plankton is the most common life form in the ocean.

A: What is the most common life form in the ocean?
****
Q: Compression zones is the opposite of rarefaction zones, where air molecules in waves are loosely packed.

A: What is the opposite of rarefaction zones, where air molecules in waves are loosely packed?
****
Q: Certain anaerobic parabasalid species exist in the digestive tracts of termites and wood-eating cockroaches, where they contribute an essential step in the digestion of cellulose.

A:
Certain anaerobic parabasalid species exist in the digestive tracts of termites and wood-eating cockroaches, where they contribute an essential step in the digestion of this?
****