The term Obligate anaerobes represent such microorganisms which can survive only in the absence of oxygen, i.e. presence of oxygen in their surrounding environment acts as a poison for them. Methane bacteria also called as methanogens are methane-producing bacteria which are obligate anaerobes as their metabolic processes do not require oxygen. Spirogyra are the green algae which produces oxygen. Pisum Sativum is commonly known as Green pea, which is a vegetable. Onion is also a vegetable.
The correct answer is D.