In paragraph 4, "transmission" refers to the process of transmitting a virus, infection, etc. Therefore, the correct answer is:
b - a conversion of power.
However, it's important to clarify that the term "transmission" in this context specifically relates to the transfer of pathogens rather than the transfer or conversion of power. If the intention was to align with the meaning given in the context of infection, an option that specifically aligned with transmitting illnesses or infections would be preferred, but it seems like the listed options may not reflect that.