A newly discovered virus with single$-$stranded nucleic acid molecule is found to contain both uracil $($U$)$ and thymine $($T$).$ Which of the following is the most likely explanation for this unusual observation?

A$.$ The molecule is a product of RNA editing, where cellular enzymes have modified the RNA sequence after transcription.

B$.$ The molecule is a hybrid of DNA and RNA, formed through a novel replication process.

C$.$ The molecule is a contaminant from a different organism, accidentally introduced during sample preparation.

D$.$ The molecule is a synthetic construct, artificially created in a laboratory setting.