The 5-carbon sugar is usually represented by a pentagon shape (which would likely be the gray pentagon in the middle if the diagram follows conventional representation). The phosphate group is often represented by a circle (which would likely be the blue circle in the diagram). The nitrogenous base is typically depicted as a complex structure with rings.
In a nucleotide, the components are:
A 5-carbon sugar (deoxyribose in DNA),
A phosphate group, and
A nitrogenous base.
So, the labels should be placed as follows:
The blue circle should be labeled as "phosphate group."
The gray pentagon should be labeled as "5-carbon sugar."
The green structure marked with "A" should be labeled as "adenine," which is a type of nitrogenous base.