Lucille is finding it difficult to play soccer after school. Her doctor thinks that her cells might not be getting enough oxygen. When Lucille talked about it with a friend, her friend said there might be a problem with Lucille's respiratory system or circulatory system. What do Lucille's cells need in order for her body to function properly? How might a problem with Lucille's respiratory system or circulatory system make it difficult for Lucille to play soccer?

In 2009, a flu pandemic was believed to have originated when viral transmission occurred from pig to human, thereby earning the designation, "swine flu." although pigs are thought to have been the breeding ground for the 2009 virus, sequences from bird, pig, and human viruses were all found within this newly identified virus. what is the most likely explanation of why this virus contained sequences from bird, pig, and human viruses? a) the virus was descended from a common ancestor of bird, pig, and human flu viruses. b) the infected individuals happened to be infected with all three virus types. c) related viruses can undergo genetic recombination if the rna genomes mix and match during viral assembly. d) the human was likely infected with various bacterial strains that contained all three rna viruses.