Microbial fuel cells are considered a sustainable source of energy. Why ? 1. They can produce electricity from certain substrates using living organisms as catalysts. 2. They use a variety of inorganic materials as substrates. 3. It can be installed in waste water treatment plants to purify water and generate electricity. Which of the above statement(s) is/are correct?

• A. only 1
• B. 2 and 3
• C. 1 and 3
• D. all these