Why Can't Scientists Just Inject the Desired Genes into an Animal

Why can't scientists just inject the desired genes into an animal or plant cell to transform it?

A) Foreign DNA in a plant or animal cell would get digested so it could never function.
B) The chromosomes in plants and animals are more complicated than those in bacteria.
C) Bacteria have enzymes that make any DNA fragment functional.
D) Viruses would get injected too and kill the cell.
E) Cells are too small to inject anything into.
"Life Application" From Teosinte to Maize