Indicate whether each of the following descriptions better applies to bacterial (B), fungal (F), protozoan (P), or viral (V) pathogens. Your answer would be a four-letter string composed of letters B, F, P, and V only, e.g. FFFB.
( ) They cannot be all grouped neatly into a single phylogenetic tree.
( ) They have the most complex life cycles.
( ) They are essentially fragments of nucleic acid wrapped in a protective shell of proteins and (in some cases) an outer membrane.
( ) They are responsible for diseases such as polio and smallpox.