Study the given classification chart.
Select the option that correctly identifies P, Q, R and S.
AP-Joint; Q-Small intestine; R-Liver; S-Anus
BP-Windpipe; Q-Skull; R-Lung; S-Blood vessels
CP-Small intestine; Q-Anus; R-Lung; S-Spinal cord
DP-Skull; Q-Brain; R-Muscle; S-Heart