The correct option is B Trichoderma
The use of biological methods for controlling plant diseases and pests is called biocontrol.
The biocontrol agents are living organisms that are very selective about the organisms they target, preferably sticking to a particular group of target organisms.
Trichoderma is a free-living fungus found in many root ecosystems. It is used as a biocontrol agent as it is highly effective in controlling several plant pathogens.