Answer:
C) The cells of the new unknown microorganism may be too small to see with the objective and ocular lenses you used.
Step-by-step explanation:
A microscope can visualize the microbes of various size only when the suitable lens with the required resolving and magnification powers are used. In the given experiment, control slides were observed under the microscope but the cells of the unknown organism were not visible. This means that the sample contained the microbial cells of a very small size that could not be seen with 40X and 10X lenses. The use of lenses with more magnification power would have helped here.