Which statement BEST describes how muscles respond to weight training? A Weight training stretches the muscles limits and makes the muscles longer
B Weight training pushes the muscles' abilities, making the muscles gain endurance
C Weight training stimulates the muscles and causes the muscle fibers to sit closer together
D Weight training overloads muscles, which causes the body to respond by making muscle fibers
larger

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.