The free-living fungus Trichoderma can be used for:
biological control of plant diseases
controlling butterfly caterpillars
The correct option is B biological control of plant diseases Trichoderma species are free living fungi that are very common in the root ecosystems. They are effective biocontrol agents of several plant pathogens like Fusarium, Phytopthora etc and used in the treatment of plant diseases.
So, the correct answer is 'biological control of plant diseases'