Tree bark is made up of plant cells
Soil bacteria is made up of prokaryotic cells
Fingernails are made up of cells.
Hence the only possible option is river water which is made up of H2O along with other microorganisms
Hope this is going to help you.
<em>Examples of a nonspecific external response to infectious agents and harmful bacteria are the following;</em>
Mucus, saliva, and tears.
They are nonspecific external responses that help to prevent pathogens from entering our bodies.
The specifics contain types of enzymes that break down the bacterial cell walls. An external response of Mucus tends to trap pathogens as well.