Final answer:
The statement is true; Group IV RNA phages have a single positive-sense strand of RNA, which can directly act as mRNA.
Step-by-step explanation:
The statement that RNA phages contain only a single positive-sense strand of RNA is true. RNA phages, specifically those belonging to Group IV of the Baltimore classification system, have single-stranded RNA (ssRNA) with a positive polarity. This indicates that their RNA can directly serve as mRNA for the synthesis of viral proteins. The replicative process involves forming replicative intermediates, which include full-length negative RNA strands serving as templates for producing more positive-strand genomic RNA.