For a physician, treating a biofilm infection in a patient poses a significant challenge compared to treating an infection with planktonic bacteria. This is due to the fact that________.

A) the biofilm likely contains several different species of bacteria living in a thick, extracellular matrix that cannot be treated by routine antibiotic therapy
B) planktonic bacteria and biofilm bacteria activate the same genes
C) despite being a thick layer, the pH remains constant throughout the biofilm making the deep layers hard to penetrate
D) planktonic bacteria secrete quorum-sensing proteins that interfere with the actions of the antibiotic