In a micro-injection, recombinant DNA is directly injected into the nucleus of an animal cell.
In another method, suitable for plants, cells are bombarded with high-velocity micro-particles of gold or tungsten coated with DNA. This method is known as biolistics or gene gun.
So, the correct option is ' Retroviruses in animals have the ability to transform normal cells into cancerous cells. In microinjection, cells are bombarded with high velocity microparticles of gold or tungsten coated with DNA'.