Which of these is part of a virus's structure?
A.) genetic material
B.) capsid
C.) protein unit
D.) pili

Genetic material, capsid, protein unit are all parts of a virus's structure.

Explanation:

Structurally, a virus is composed of three main units – the nucleic acid genome, a protein unit or covering called capsid, and a lipid layer.

The nucleic acid genome consists of the DNA and the RNA, both of which stores the genetic information. When a virus enters a host’s body, it reprograms the host based on the genetic information stored in this genome molecule.

The genomes are protectively placed inside a capsule called protein shells called capsid. The shapes of a viral capsid may be helical (like tobacco mosaic virus) or icosahedral (like polio virus). Many polypeptides unite to form the protomers or the capsomers of the capsid.

When a virus is covered by a lipid layer it gains an envelope-like structure.

When a virus is complete with all these essential structures, it is called as virion.  

Pili are microfilamentous structures present in bacteria.