Cyanobacteria have been engineered to produce isobutanol directly. what advantage does this have over other alternative biofuels

There exists the same question that has the following choices.

a. It is an inherently renewable fuel source.
b. Multiple processing steps can be avoided.
c. They produce chemical energy through photosynthesis.
d. They make a biofuel alternative to gasoline.

The correct answer is letter b. Multiple processing steps can be avoided.