Are viruses alive? This question is debated among scientists throughout the world. Consider the following passage. Scientific researchers discovered agents that behaved like bacteria causing diseases such as rabies and hoof-and-mouth, but were much smaller. At this time it became the general view that viruses were biologically "alive." This perception changed in 1935 when the tobacco mosaic virus was crystallized and scientists demonstrated that the particles lacked any mechanisms necessary for metabolic function. It was determined that viruses consisted of a nucleic acid, DNA or RNA, surrounded by a protein shell and the scientific view changed: viruses are complex biochemical mechanisms but not alive.

According to the passage, the MOST IMPORTANT evidence supporting the opinion that viruses are not alive is that they

Acause disease.

Bcontain DNA or RNA.

Care much smaller than bacteria.

Ddo not have a cellular structure.