Bacteria that contain recombinant plasmids can be easily isolated because: select one:

a. they are designed to be resistant to certain antibiotics
b. their colonies will be distinguished by a color variation from those colonies containing non recombinant plasmids
c. they are smaller than non-recombinant bacteria
d. they are larger than non-recombinant bacteria

The correct answer is a. they are designed to be resistant to certain antibiotics

Explanation:

Recombinant plasmids are those bacteria in which a foreign genetic material is placed for giving some addition characteristic to the plasmid. The recombinant plasmid must have origin or replication and a selectable marker. It should produce its numerous copy in its host.

So most of the plasmids have antibiotic-resistant gene as selectable marker. So the bacteria transformed with the recombinant plasmid can be isolated from other bacteria by growing them on medium containing the antibiotic that the recombinant plasmid in bacteria has.

For example, bacteria having a recombinant plasmid that contains an ampicillin-resistant gene can grow in medium having ampicillin antibiotic but other bacteria that do not have this gene can not grow.