(nine 0 1 nine? Laiwu) scientists drop the G juice of G tobacco with mosaic disease on healthy tobacco leaves, causing mosaic disease; Juice of diseased tobacco leaves

Viruses, like all living things, have heredity, variation and evolution, and are a very small life form with extremely simple structure. Viruses have no cell structure, and are mainly composed of internal nucleic acid and external protein shell, so they cannot survive independently. They can only carry out life activities if they are parasitic in living cells. Once they leave, they become crystals. Viruses can only use the ready-made metabolic system in the living cells of the host to synthesize their own nucleic acids and protein components. Its mass reproduction is achieved by assembling elements such as nucleic acid and protein. Scientists drop the juice squeezed from tobacco with mosaic disease on healthy tobacco leaves, which leads to mosaic disease. After the juice of sick tobacco leaves passed through the bacterial filter, it dripped on healthy tobacco leaves, still causing mosaic disease, from which 9 viruses were found. The above virus discovery experiments can't conclude that bacteria are pathogenic.

So choose 7.