One Feature of "Engineered" Plasmids That Is Helpful in the Isolation

One feature of "engineered" plasmids that is helpful in the isolation and analysis of cloned DNA is:

A) they can only handle DNA fragments of up to 10 kb.
B) that they are an integral part of all eukaryotic cells.
C) they contain no genetic material of their own so that the cloned fragment is truly isolated.
D) the presence of genes that allow transformed cells to survive on different media.
E) the base sequence of one strand reads the same asits complement