Which of the following statements is true? Opportunistic bacteria only cause infection under certain conditions. Most bacterial infections are caused by bacteria already in the body. The flu and the common cold are treated with rest, fluids, and antibiotics. Leukocytes are the first line of defense against pathogenic microorganisms.

How is ribosomal rna useful as a molecular clock? a. a large portion of the dna ring is not vital to structure or function, allowing it to accumulate neutral mutations. b. its rate of mutation increases over time as organisms continue to evolve and differentiate from each other. c. a slow mutation rate makes it useful for determining evolutionary relationships between ancient species. d. it is only found in select organisms, making it easier to compare relationships between species that have it.

Why do we perceive objects as retaining their brightness under different lighting levels?

Ecology can best be described as the study of what