Given a scientific passage and an answer, generate a question for the given answer.

Let me give you an example: Passage: A frameshift mutation is a deletion or insertion of one or more nucleotides that changes the reading frame of the base sequence. Deletions remove nucleotides, and insertions add nucleotides. Consider the following sequence of bases in RNA:. Answer: nucleotides.
The answer to this example can be: A frameshift mutation is a deletion or insertion of one or more of what that changes the reading frame of the base sequence?
Here is why: The science passage defines frame mutation and the main compoment here is nucleotides. Hence the generated question is apt.

OK. solve this:
Passage: Biomass is another renewable source of energy. Biomass includes wood, grains, and other plant materials or waste materials. People can burn wood directly for energy in the form of heat. Biomass can also be processed to make biofuel. Biofuel is a fairly new type of energy that is becoming more popular. Biomass is useful because it can be made liquid. This means that they can be used in cars and trucks. Some car engines can be powered by pure vegetable oil or even recycled vegetable oil. Sometimes the exhaust from these cars smells like French fries!. Answer: biofuel
Answer:
Biomass can also be processed to make what kind of fuel?