People entering the U.S. first need to get a visa. A visa allows the visa holder to travel to a port of entry in the United States and request the immigration officials permission to enter the country. The visa could be a non-immigrant visa if the person intends to stay in the U.S. temporarily.
Tobacco mosaic virus (TMV) is a positive-sense single stranded RNA virus that infects a wide range of plants, especially tobacco and other members of the family Solanaceae.The infection causes characteristic patterns, such as  mosaic -like mottling and discoloration on the leaves (hence the name).TMV was the first virus ever to be discovered.Although it was known from the late 19th century that an infectious disease was damaging tobacco crops, it was not until 1930 that the infectious agent was determined to be a virus.lthough it was known from the late 19th century that an infectious disease was damaging tobacco crops, it was not until 1930 that the infectious agent was determined to be a virus.
The first virus was made in Chauburji, Lahore, Pakistan, 1986. Two programmers named Basit and Amjad Farooq Alvi, .replace the executable code in the boot sector of a floppy disk with their own code designed to infect each 360kb floppy accessed on any drive.Infected floppies had Â© Brain for a volume label.iruses have a long history. The first recognised one was called the Creeper Virus. It was designed in 1971 by Bob Thomas at BBN Technologies. It was a self replicating progra â¦ m that got out of hand infected the companies computers and got out onto the Arpnet before it was halted.