Koilocytes are characteristic of
cells infected with human papillomavirus
cells infected with herpes simplex virus 2
cells infected with all forms of herpesviruses
cervical cancer cells

Cells infected with human papillomavirus.

Explanation:

Koilocyte is a type of squamous epithelial cell that has a number of structural changes, which leads the cell infected by human papillomavirus. Koilocyte have many cellular changes like:

Human papillomavirus (HPV) is the most common sexually (active) transmitted infection. Sometimes it can be transmitted during birth (from mother to the child).  

it's diluted or concentrated

in a diluted solution, you can add a lot more solute but in concentrated only a little more can be added