It was very difficult however to understand how the genetic information of viruses containing RNA could form a part of the hereditary material of the tumour cells.
(It; was; very difficult however to understand how the genetic information of viruses containing RNA could form a part of the hereditary material of the tumour cells) (viruses; containing; RNA)
It viruses
was containing
very difficult however to understand how the genetic information of viruses containing RNA could form a part of the hereditary material of the tumour cells
RNA