Which of the following is not a way in which humans rely on prokaryotes?

Since there are no written choices, I could guess that prokaryotes are not reliable when it comes to diseases and other forms of ill-causing behavior of these microorganisms.

Scientists rely on prokaryotes to examine their structure and functions in order to come up with a good medicine. Some rely on prokaryotes to do the natural processes of decomposing and recycling matter throughout the earth's spheres.