Scientists have learned the full extent of viral abundance on earth because _______.

A) viruses are known to grow on all life forms: animal, plant, fungi, and bacteria
B) metagenomic sequencing has identified viruses in a broad variety of environments
C) the final step of the viral life cycle, release of mature viruses and cell lysis, releases millions of viruses
D) a wide variety of microbes is available to act as hosts for these viruses