Right option is (a) 8 – Azaguanine
Best explanation: The myeloma cells harvested from the antigen injected mouse has to be added with 8-Azaguanine. 8-Azaguanine tends to stop the de novo pathway of and the cells which cannot survive will die. Myeloma cells which are HGPRT- will be the only cells growing in the culture due to the presence of the compound. These cells will have high viability and rapid growth.