Examination of your slide will show that a few nuclei do not appear next to a cell wall

The onion root tips are very famous for observing the distinct phases of mitosis as the chromosomes are very large and get very dark when stained.  

The epidermal cells in the onion take place cell division (cytokinesis) and mitosis (nuclear division). The interphase cell usually possesses one or number of nuclei, thus, a few nuclei are not witnessed adjacent to a cell wall.  

The answer on ED:

D: "the process of hypothesis and testing through which scientific inquiry occurs"